Features of lithological composition and reservoir properties of horizonsVII+VIIILower Oligocene age in the White Tiger oil field (Vietnam)

Bui Khak Hung

National Research Tomsk Polytechnic University, Tomsk

Scientific supervisor associate professor

The White Tiger field is a unique field in Vietnam in terms of oil reserves. It is located on the shelf of southern Vietnam, 120 km southeast of the coastline. The geological section of the deposit is represented by pre-Cenozoic crystalline rocks of the basement and Cenozoic terrigenous rocks of the sedimentary cover, in which sandy-silty and clayey rocks of the Oligocene, Neogene and Quaternary age are distinguished. The greatest variability in thickness and composition is characteristic of the basal Lower Oligocene deposits, which pinch out on the slopes of basement blocks occupying a high hypsometric position. Among the Lower Oligocene deposits, horizons VII+VIII are the most oil-saturated and belong to oil deposits of industrial importance. Therefore, studying the features of the lithological composition and reservoir properties of horizons VII+VIII is of great importance.

Using the Surfer program, a structural map was constructed along the top of the VII+VIII horizons of the Lower Oligocene and modeled it in 2D (Figure 1A).

(A) (B)

upper – well / lower – elevation (m) upper – well / lower – thickness (m)

Rice. 1.Structural map (A) and isopach map (B) of horizons VII+VIII of the lower

Oligocene of the White Tiger deposit

Figure 1A shows that the drawing of structural maps of the northern section (horizons VII+VIII of the Lower Oligocene) of the White Tiger deposit changes greatly. In well 1013, the lowest elevation was discovered -4161 m along the roof and -4225 m along the base, that is, a depression zone is noted in the eastern direction. And the highest elevation is -3336 m along the roof and -3381 m along the base in the northwest in well 4, in the area of ​​which the arch of the structure is clearly visible. The amplitude of the dome is 470 meters along the contouring isohypsum - 3850 m. For a visual representation of the power distribution, an isopach map was constructed. (Figure 1B)

Figure 1B shows a northeast-trending disjunctive fault. It can be seen that the maximum thickness reaches 94 m in well 10 and is represented by sandstones of continental origin. And the minimum thickness is 22m and 17m in wells 64 and 83, in the western part of the site.

The formation of sediment thickness is possible in two directions of sedimentation conditions. The reduction in the thickness of sediments in the arch and its increase on the wings of the uplifts is due to the erosion of this elevation and the filling of the depressions with destruction products.

An increase in the thickness of sediments on the slopes of paleo-uplifts indicates the accumulation of sediments in the shallow water zone during wave activity.

Using the methodology developed and well logging data, maps of lithological composition and sand content were constructed (Figure 2).

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( A) (B)

upper – well upper – well

lower – sandiness coefficient (%) lower – αPS value

right – clasticity coefficient (%) right – thickness (m)

Rice. 2. Map of sandiness and clasticity coefficients (A) and map of lithological composition (B) of horizonsVII+VIIILower Oligocene (0-0.2: clays and silty-clayey rocks; 0.2-0.4: siltstone and clayey-silty rocks; 0.4-0.6: mixed sandy-silty-clayey rocks; 0.6 -0.8: Fine-grained sandstone; 0.8-1: coarse-medium-grained sandstone, non-clayey)

Figure 2A shows the distribution of type A reservoirs (PS value in the range of 1-0.8) in the area of ​​wells 83, 64, 4, 14, 602, 1014, 1003. The distribution zone of type B reservoirs (PS value in the range of 0.6- 0.4) in wells 10, 1013. The distribution zone of type B reservoirs (0.6-0.8) in wells 114, 116, 907. The distribution zone of non-reservoirs is identified in the east, northeast (well 9), in the south ( wells 1106, 12).

In Fig. 2B we see that the zone of high occurrence of sand bodies is located in the area of ​​wells 14; 116 and 1014 with an average thickness of 23 m. The maximum value of the sand content coefficient is in well 1014 and corresponds to 70.2%. The maximum value of the clasticity coefficient is also observed in the well of 1.3%). The decrease in the sandiness coefficient on the arch and its increase on the slopes and at the foot of the uplifts is due to the activity of flows that erode the hills and form cones of erosion products.

Along the line of wells 16-9, a geological profile of VII+VIII horizons of the Lower Oligocene was constructed (Figure 3).

Rice. 3. Geological profileVII+VIIILower Oligocene horizons in the White Tiger oil field (Vietnam) along the line of wells 10 – 14 – 145 – 116 – 9

Horizons VII+VIII represent an anticlinal fold complicated by faults. On the profile we see the change in the thickness of the horizons across the wells. In well 10, the thickness of sediments reaches 94 m. And in well 14, the thickness of sediment decreases to 33 m. A fault is noted between wells 14 and 145. And between wells 116 and 9, 2 faults were identified, characterized by a significant width of the rock crushing zone. The lithological composition of the sediments is heterogeneous. In well 10 we see an alternation of clay and sandy-silty rocks. The thickness of the clay is 40 m. Clay deposits pinch out and completely disappear in well 14. In well 14, only sandy-alveurite rocks with a thickness of 33 m are observed. Clay deposits are observed in wells 145, 116 and the thickness of clay increases in well 9. Clays lie within the sandy horizon as a layer. The thickness is insignificant in comparison with the thickness of sandstones and amounts to 6-7 m. In well 9, the thickness of the clay layer increases by 2 times. On the profile we mark the zones of the highest reservoir properties in wells 14, 145, 116, in which the porosity coefficient varies from 12% to 14% and the oil saturation coefficient is 0.6-0.66 units. Of all the studied wells, the highest oil flow rate was obtained in the m3/day well. With such low porosity values ​​(practically non-reservoir), high oil flow rates can be explained by the proximity of zones of two tectonic faults.

Thus, a complex type of rock reservoir of porous-fractured horizons VII+VIII has been identified in the northern block of the White Tiger field. High oil flow rates were obtained in wells drilled close to zones of tectonic disturbances. In wells that have only a porous reservoir type and are far from zones of disjunctive faults, much lower oil flow rates were obtained.

Bibliography:

1. P, G, et al. Geology and oil and gas potential of the Sunda shelf basement. M., Oil and Gas, 1988, 285 p.

2. Ezhova interpretation of geophysical data; Tomsk Polytechnic University. – 3rd ed. – Tomsk: TPU Publishing House, 200 p.

3. Pospelov foundation: geological and geophysical methods for studying reservoir potential and oil and gas content - Moscow 2005.

FEDERAL EDUCATION AGENCY
State educational institution of higher professional education
"TOMSK POLYTECHNIC UNIVERSITY"

White Tiger deposit

Completed by: student gr.2B33
Zhdanova M.P.
Checked by: Valevsky V.V.

Tomsk 2005

1. An alternative model for the formation of an oil deposit in the basement of the White Tiger field…………………………………………….…...………3

2. Structure of the shelf of South Vietnam……………………………...……… ….7

3. Composition and age of basement rocks…………………………………….………….8

4. The nature of the voidness of the oil-containing foundation of the White Tiger field…………………………………………………………………………………….……….12

4.1. Secondary changes in basement rocks…………………………………..12

1. Tectonic activity………………………………………………………...12
2.Hydrothermal activity…………………………....………....12

5. Distribution of reservoirs of the White Tiger field and assessment of their filtration and capacitance properties…………………………………………………………….….15

5.1. Separation of rocks by types of voids…………………………….…...16
5.2. Interpretive model of reservoirs…………………………….…..16
.
6. Oil content of granitoids in the basement of the White Tiger field………….18

7. Field and geological features of the structure of the reservoir and the foundation deposits of the White Tiger field……………………………………….…20

Conclusion………………………………………………………………………………….…24
References…………………………………………………………………………………25

1.An alternative model for the formation of an oil deposit in the basement of the White Tiger field
The discovery in 1988 of a unique oil deposit in the granitoids of the basement of the Vietnamese shelf (White Tiger field) gave a tangible impetus to the development of theoretical thought in the geology of oil and gas, technical and technological solutions for its industrial development.
One of the controversial questions, to which a definitive answer has not yet been found, is the origin of the oil itself, which forms a deposit in fractured granites. It is traditionally believed that oil migrated into the granite massif from adjacent terrigenous Lower Oligocene deposits. The rationale for this assumption is contained in the dissertations of Kh.D. Tiena (1999) and V.L. Shuster (2001). According to these authors, the oil and gas potential of the Lower Oligocene deposits is quite sufficient to “feed” the reservoir under consideration, the initial geological reserves of which exceeded 500 million tons. In particular, VL. Shuster argued that for this it is enough that there is an oil collection area with a radius of 30 km around the protrusion of the foundation of the White Tiger field.
In order to verify the reality of the proposed mechanism of formation of the deposit, the authors carried out a control calculation of the potential mass of hydrocarbons produced by the Lower Oligocene and the lower strata of the Upper Oligocene sediments within the oil collection area adjacent to the studied granite foundation protrusion. It is based on a structural map of the Cuu Long depression along the basement surface at a scale of 1:25000 (see figure), as well as seven time seismic profiles oriented across the strike of the uplift under study.
The boundaries of the possible oil collection area are determined on the structural map. Analysis of time sections made it possible to determine the thickness of the deposits of the lower and lower strata of the Upper Oligocene along the entire perimeter of the field, taking into account the average sand content coefficients, the volume of clayey rocks of these strata, identified as the main oil source objects, was calculated. It has been established that sand bodies do not form extended layers, but have a lens-shaped configuration. The length of the lenses does not exceed 10-12 km and, as a rule, they do not communicate with each other.
Along with determining the physical parameters of the “parent strata” of Oligocene age, numerous data on pyrolysis, vitrinite reflectivity, temperature-time (TP) and other organogeochemical indicators of Oligocene clay deposits developed within the blocks adjacent to the White Tiger and...

History Block 09 -1 Unique deposits “White Tiger” and “Dragon”. JV Vietsovpetro (Viet. Sovpetro) is a joint venture of the Russian company Zarubezhneft OJSC and the Vietnamese company Petro. Vienam", created in 1981. Bach Ho (Vietnamese Bạch Hổ, Russian White Tiger) is a large offshore oil field in Vietnam, located 120 km southeast of the port city of Vung Tau, on the shelf of the South China Sea. 2

Characteristics of the deposit 1) tectonic disturbance; 2) hydrocarbon deposit of sedimentary cover; 3) the MBT well is located within the Cuu Long depression, its length is 450–500 km, width 75–110 km. Most wells drilled on the foundation are high-yield. The maximum exposed thickness of the foundation reaches 1700 m, the thickness of the sedimentary cover exceeds 4300 m. The lower boundary of the deposit is established conditionally; well BT-905, drilled to an absolute depth of 5014 m, did not penetrate the oil-water contact. 3

Characteristics of the field Magmatic and fractured basement reservoirs of Mesozoic age are widely developed within the shelf of southern Vietnam. In 1988, during re-testing of the MSP-1-1 well at the White Tiger field in the Cuu Long Depression, an oil gush was obtained for the first time from a depth of 3150 m. The discovery of a unique deposit in fractured granitoids of the Mesozoic basement has intensified exploration work on the formations of the magmatic basement on the shelf of Vietnam and the region as a whole. 4

More than 120 exploration, production and injection wells have been drilled into the field. On the Central arch, a larger number of wells were drilled to depths of 4500 -4760 m. On the Northern arch - 4457 m. The deepest well BT-905 was drilled to a depth of 5014 m. In 1988, the first million of oil was extracted. 2005 – 150 million tons of oil. 2008 – 170 million tons of oil. By the end of 2009, accumulated production amounted to 183 million tons. 2012 – 200 million tons of crude oil – “White Tiger” and “Dragon” fields. In 2012, Vietsovpetro's production amounted to 6,110 thousand tons, including White Tiger - 4,398 thousand tons, Dragon - 1,504 thousand tons.

Properties of oil Oil from the Vietnamese fields of Bach Ho and Rong, in terms of their rheological properties, have a common characteristic: high viscosity and high wax content. The pumping and transport of such oils indicate that in oil pipelines laid under water, intense heat exchange between the flow of pumped oil and the environment leads to a sharp change in the thermohydrodynamic regime in the flow along the pipeline. The drop in oil temperature along the way causes a change in its rheological properties and is accompanied by phase transitions, as a result of the saturation of the flow with heavy hydrocarbons, as well as the formation of near-wall oil deposits on the inner surface of the pipeline. These factors, under certain technological conditions, turn out to be the cause of a gradual spontaneous decrease in pipeline capacity, which, first of all, increases energy costs for pumping, and therefore increases the cost of pipeline transport. Oil produced in the country's fields is characterized by a low sulfur content of 0.035–0.14% (in Brent it is 0.2-1%, and in Urals 1.2-1.3%). 6

Field development The following were built at the White Tiger and Dragon fields: 13 offshore stationary platforms 22 conductor blocks 2 technological platforms - maximum productivity: 38 thousand tons per day for oil, 46 thousand tons per day for gas-liquid mixture. 3 compressor stations with a capacity of 9.8 million cubic meters per day. A unified low-pressure gas collection system ensures the normal functioning of the entire technological process for collecting and transporting gas to the shore, preparing gas-lift gas and using it for mechanized oil production at the fields of the Vietsovpetro joint venture, and also allows for the utilization of up to 97% of the produced gas. The Vietsovpetro JV has created one of the best onshore bases in Southeast Asia for the construction and offshore installation of technological and satellite platforms for well drilling and oil and gas production. The Vietsovpetro JV has four jack-up drilling rigs, more than 20 fleet units, including crane-mounting, fire-fighting, diving and transport-tug vessels, and four berthless loading units.

Pipeline from the Dragon field At the end of 1994, a pipeline was successfully put into operation from the production platform RP-1 of the Rong field to the Central Process Platform TsTP-2 of the Bach Ho field, laid along the bottom of the Vietnamese shelf, with a length of 33 km for pumping highly paraffinic oil with a pour point of 250 C. To improve the rheological properties of this oil, the depressant additive Sepaflux ES-3266 produced by the BASF concern is used. At the same time, it was possible not only to significantly lower the pour point, which ensures reliable pumping of crude oil through an underwater non-thermal insulated pipeline, but also to reduce the plastic viscosity of oil by more than 7 times. 9

Field development Installation of moored loading “Vietsovpetro-01” - crude oil storage tanker Full load - 139 thousand tons of oil 9 anchors 10 -15 inclined shafts Lateral divergence of more than 2 km 10

Oil refining in Vietnam The only operating oil refinery in the country is the Dung Kuat Refinery. Construction of a refinery is currently starting in the north of the country and construction is planned in the south. The Dung Kuat refinery was built in three years (from November 2005 to January 2009), and launched in February 2009. The Nghi Son refinery was planned for construction in the north of the country; its capacity, according to the basic design, was 10 million tons per year. Commissioning was planned for 2013–2014. The Long Son refinery will be located in the south of the country, its design capacity is also 10 million tons per year. The project is at an early stage of development, partners and investors have not been identified. Commissioning is planned for 2016–2020. eleven

Block 09 -3/12 is located in Yuzhno. Kon Son oil and gas basin, 150 km southeast of Vung Tau and 20 km east of the White Tiger field. Oil and gas prospects are associated with Oligocene-Miocene deposits and crystalline basement rocks. It is planned to process and interpret previously conducted seismic studies, assess the oil and gas potential of promising structures of the block and prepare for drilling the first exploration well. Due to the fact that the Sea Turtle field is located in the overlap zone of block 09 -3 with the Southern Dragon field of block 09 -1 , a decision was made to unite the two fields into a Joint Activity Zone. In 2010, stable industrial oil production began at the combined Southern Dragon - Sea Turtle field, which reached 12 one million tons in 2013.

Block 04 -3 is located 280 km southeast of Vung Tau. The Tien Ung - Mang Kau field was discovered within the block. The oil and gas potential of the block is associated with Oligocene and Lower Miocene deposits on the Bo Cau, Hoang Hac and Kim Loan structures prepared for drilling. In 2013, drilling of an exploratory well began on the Bo Kau structure. Block 04 -1 is located in the north of the South Con Son basin, 250 km southeast of Vung Tau. In 2012, the exploration well ST-2 X was drilled at the Son-Tien-B structure. Taking into account the drilling results, special processing and interpretation of seismic data is carried out to identify and prepare for drilling promising objects. 13

Block 42 is located in the Phu Quoc oil and gas basin within the Gulf of Thailand, 400 -450 km west of Vung Tau. Oil and gas prospects are associated with the Paleozoic-Mesozoic complex. An oil contract was signed under the terms of a PSA. At the stage of preparation is the “Joint Activity Agreement” between the Vietsovpetro JV and the PVEP company (a subsidiary of Petrovietnam KNG). Block 12/11 is located within the Yuzhno. Con Son oil and gas basin, 350 km south-east of Vung Tau. Petroleum potential is associated with Oligocene and Lower Miocene deposits within the identified Thien Nga, Chim Cong, Chim Ung, Hong Hac/Hoang Yen and Quyt structures. To carry out prospecting and exploration drilling in 2013, 3 D seismic survey work is planned on the block. 14

15

The uniqueness of the Vietnamese shelf is the discovery of large deposits in granites.

Vietnam's oil and gas industry is very young. Even before the Civil War, some American companies, e.g. Mobile, unsuccessfully tried to find oil in Vietnam. Soviet oil workers here for the first time used the practice of drilling not at 500-600 m, as was usually done, but at 3,000 m, trying to discover oil and gas reserves in deep rocks.

In 1983, with the direct assistance of the Soviet Union, the first significant oil field, Bakhkho ( White Tiger- “White Tiger”). Its industrial exploitation began in 1986. The first gas well was laid in the same area and produced results in 1994. As a result of intensive geological exploration work over the next 12 years, it was established that the subsoil of Vietnam has a sufficiently high potential to provide the country with energy resources and allow it to enter the world oil market as an exporter. According to VR Amoco Statistical Review of World Energy for 2001, confirmed oil reserves on the continental and shelf parts of the territory of Vietnam are estimated at 100 million tons, and natural gas reserves at 190 billion m 3 (Fig. 1).

Currently, only the oil and gas industry exists in Vietnam, and the country's leadership is persistently pursuing the creation of processing enterprises. International tenders are announced for each proposed project. The winner enters into a production sharing agreement (PSA). Vietnam provides its land and resources, while the foreign partner provides equipment and technology for a specific project. After this, the produced products are divided in percentage terms in accordance with the signed agreement, and if previously the foreign partner was allowed to have no more than 15–20% of the shares of the joint venture, now it is allowed to own a 50% stake. It is also possible to repay the cost of depreciation of equipment owned by a partner company that produces oil.

Rice. 1. Map of the Vietnamese shelf with the location of hydrocarbon fields (Areshev, 2003): 1 – spreading zones; 2 – isobaths of the seabed, m;

Yes, a state company PetroVietnam has already concluded more than 30 contracts totaling over $2 billion with leading foreign companies: Unocal, Mobile, Conoco, British Gas, British Petroleum, Statoil(Norway), Petronas(Malaysia), Anzoil(Australia – New Zealand), Idemizu(Japan) and Shell.

Soviet-Russian-Vietnamese cooperation

There are two joint ventures operating on the Vietnamese market: VietSovpetro(50/50) and VietRoss. With their direct participation, the construction of a large oil refinery and an 800-kilometer oil pipeline began in the Dung Quat region (Quang Ngai province), the cost of the project is $1.3 billion. The plant's capacity should cover 65% of the country's needs for petroleum products such as propylene, liquefied associated gas, diesel and aviation fuel. The term of the agreement is 25 years. The Russian-Vietnamese joint venture is the de facto monopolist on the Vietnamese oil market. VietSovpetro– it accounts for 90% of the oil produced in the country. The Vietnamese have made no attempts to curtail cooperation; on the contrary, they intend to expand it.

VietSovpetro was created 20 years ago, when an agreement was signed between Zarubezhneft and the state company PetroVietnam on the start of development, with the assistance of the Soviet side, of oil fields on the shelf off the coast of South Vietnam. In 1986, the field with the exotic name “White Tiger” produced its first oil. Now the average annual oil production is 13 million tons, the growth rate is 15% per year. According to the plans of the management of the joint venture, in the next decade this figure will increase to 20–22 million tons. VietSovpetro Today it is the largest and most successful joint venture with foreign participation in the country. When the joint venture was created in 1981, its authorized capital was set at $1.5 billion, and currently its fixed capital is $2.8 billion. Total revenue from the sale of crude oil for 1991–1998. exceeded $7.5 billion, a significant part of which replenished the state budgets of Vietnam and Russia.

To work on the shelf, the Soviet Union specially built a base in Vietnam for the construction of drilling platforms (they have a total of VietSovpetro twelve). A typical socialist management project turned out to be profitable under market conditions. If foreign companies are forced to transport their platforms over distances of thousands of kilometers, then VietSovpetro collects them locally, and for other countries in the region, for example, Malaysia, and even on orders from American and British companies. It was not without the mediation of Zarubezhneft that Gazprom OJSC appeared in Vietnam. We are talking about plans to develop a gas field on the shelf of Central and Northern Vietnam with reserves, according to preliminary estimates, of 700 billion m 3. The work of the Russian gas monopolist in Vietnam begins, as in the case of VietSovpetro, with the creation of a joint venture. The new company will primarily supply gas to Vietnamese consumers, but further export to neighboring countries, such as China, is not excluded.

Undoubtedly, not only Russia is interested in the Vietnamese oil and gas potential. Recently British British Petroleum, Indian ONGC and Norwegian Statoil signed an agreement with the government of Vietnam to develop a natural gas field on the country's shelf. Over the course of 20 years, the companies undertake to supply gas to three Vietnamese power plants and invest about $1.5 billion in its production and transportation. However, the Russian side does not believe that its interests can be infringed. Russia's position in Vietnam is very strong. However, the current situation indicates that the Russian side must pursue an active and reasonable policy. Moreover, without updating the resource base in five years, production VietSovpetro may be significantly reduced.

Another fact gives Russia confidence. Recently, the parties signed documents according to which Vietnam must pay Russia (on the principles of the Paris Club of creditors) $1.7 billion over the course of 23 years. At the same time, the parties agreed that Vietnam’s debt should be repaid by investing in large interstate projects, including oil and gas.

Oil and gas fields and their use

To date, 10 main hydrocarbon reservoirs have been explored in the country, and the presence of oil and gas has been confirmed in four of them (the deltas of the Red, Mekong, South Con Son, and Tho Tu rivers). Particular attention is paid to the development of gas fields on the shelves of the Gulf of Tonkin and the Gulf of Thailand. The offshore zone of Vietnam is 327.9 thousand km 2 and five main oil fields are currently being developed on it: Bach Ho ( White Tiger) - since 1986, 150 km southeast of the city of Vung Tau, production volumes - 7 million tons per year with the prospect of increasing productivity to 8.5 million tons in 2000 and up to 13 million tons by 2005; Daihung - since 1994, with a capacity of 565 thousand tons per year; Rong - since 1994, with a capacity of 475 thousand tons per year; Bungkekwa - 755 thousand tons per year; Rangdong - with the prospect of up to 12.1 million tons per year.

However, there are still contradictions (mutual claims) with China regarding the ownership of the Paracel Islands, Spratly Islands and adjacent shelf areas, as well as the shelf of the northern part of the Gulf of Bakbo (Tonkin) and the disputed water area in the Gulf of Thailand, which is claimed by Malaysia , exploration and industrial development of about half of the promising oil and gas area remains very problematic.

The first Bahkho gas field began producing production in 1994 (a joint venture PetroVietnam – Hyundai), followed by the Tien Hai field discovered in 1970 (with a productivity of 110 million m 3 per year) and Nam Con Son. Total confirmed natural gas reserves are 190 billion m3, and projected reserves are 325 billion m3 (according to US Energy InformationAdministration as of December 1998). By the end of 2000, Vietnam increased gas production to 3–4 billion m 3 . With the assistance of an American concern Mobile A master plan for the development of the gas industry for the period until 2010 was developed.

The increase in gas production volumes is associated with the further development of the country's electricity network. The largest gas-fired power plant, Fumu, is being built, with a total capacity of 3,600 MW by 2010. The possibility of constructing a number of chemical enterprises using natural gas as a feedstock is being considered.

As is known, earlier Korean companies, in collaboration with foreign partners, discovered an oil field off the coast of Vietnam. This field, located at a depth of 47 meters, 180 kilometers northeast of Ho Chi Minh City, is believed to have oil reserves of 570 million barrels. It was planned that the net income of Korean companies would be at least $800 million, including all investment costs. In the consortium created to explore and develop Vietnamese oil fields, the Korean National Petroleum Corporation and the SK Corporation have 14.25 and 9% shares, respectively, an American company Conoco– 23.25% shares. The rest of the shares are controlled PetroVietnam– 50% and Geopetrol– 3.5%. The first drilling in the area of ​​the discovered deposit was carried out in August 2000, and additional, testing - in May 2001. Thanks to the participation of Korean companies in this project, Korea will be able to receive about 28.6 thousand tons per day, or 10% of the crude oil it needs oil from Vietnam, which will significantly reduce its dependence on oil supplies from Middle Eastern fields. Currently, Korea is forced to import 77% of its crude oil from the Persian Gulf region.

Geology and geological exploration

The shelf waters of the south of Vietnam, where the Vietsovpetro JV carried out geological exploration work, are confined to the Cuu Long and South Con Son depressions, separated by the Con Son rise. This is an area of ​​young subsidence, characterized by the accumulation of a thick layer of terrigenous and chemogenic-terrigenous sediments of Oligocene-Pliocene age. Among them, bodies of effusive rocks are quite widespread. In the most submerged areas of the depressions, the presence of more ancient Paleogene deposits is assumed. The deposits lie on the erosional surface of a heterogeneous crystalline basement composed of granitoids of various compositions. The age of the basement rocks, according to the limited data available, is Late Triassic – Early Cretaceous.

Geological study of the shelf of South Vietnam began in the late 1960s. firms Mandrel,Shell, Mobile Oil, Marathon, Pecten, and later Deminex, Agip, Bow Walley etc. Within the water area of ​​activity of the Vietsovpetro JV, aeromagnetic studies were carried out, about 30 thousand km of regional and detailed seismic profiles were worked out, and nine exploratory wells were drilled.

Systematic work on the development of oil and gas resources on the continental shelf in the south of Vietnam began in 1981 after the creation of the Vietsovpetro joint venture. The JV's operating area covered seven shelf blocks with a total area of ​​about 50 thousand km 2 . It included almost the entire Cuu Long depression and the northern part of the South Con Son depression. According to preliminary estimates, the potential geological hydrocarbon resources of this water area along the sedimentary section in the Lower Oligocene and Lower Miocene amounted to 6,200 million tons of fuel equivalent (recoverable - about 1,800 million tons). Subsequently, the area of ​​activity of the joint venture was focused on accelerated exploration and development of the White Tiger field. This was an exceptional target with oil present in the granite basement beneath the Paleogene sediments. Such a discovery in the practice of oil and gas work is considered revolutionary. After this, the water areas containing almost 60% of the initial resources in the Cuu Long depression and completely in the South Con Son basin were excluded from the scope of the joint venture’s work. However, by 1996, the joint venture had completed 63.4 thousand km of seismic surveys, including 15 thousand km of spatial (three-dimensional) surveys. 34 prospecting and exploration wells were drilled, and inflows of oil and gas were obtained from 28. 7 deposits have been discovered, three of them: White Tiger, Dragon and Daihung are classified as large. A large amount of research work has been carried out to study the geological structure and oil and gas potential of the region.

The main area of ​​work of the joint venture is the Cuu Long depression with an area of ​​about 30 thousand km 2. On the mainland side it is limited by the Chatan monocline, in the southeast by the Con Son rise. Within the basin, the Central Cuu Long and South Cuu Long troughs are distinguished, separated by the Central Uplift. In troughs, the basement surface is at a depth of 6.5–8 km, in the most elevated blocks of the Central Uplift – at a depth of 2.5–3 km. A characteristic feature of the geological structure of the depression is the presence of large, several tens of kilometers long and with an amplitude of up to 1,500–1,600 m, synsedimentary faults and normal faults, as well as numerous smaller faults. Northeast-trending faults caused the formation of the high-amplitude White Tiger horst structure, the main element of the Central Uplift. Within the Cuu Long depression, a significant number of anticlinal structures have been identified, formed as a result of multidirectional movements of basement blocks. Structures of a non-anticlinal type are widespread, associated with lithological replacements, pinch-outs, abutments of sandy-siltstone horizons to the basement, as well as with intraformational erosion.

In the South Con Son depression, Vietsovpetro carried out work only within the northern part, on the Dai Hung and Thanh Long structures. The first corresponds to a highly elevated basement block (its surface is located at a depth of 2,600 m); in the second, crystalline formations are assumed to be at a depth of more than 6,000–7,000 m.

In accordance with existing ideas about the geological structure and oil content of the Cuu Long and South Con Son depressions, the first exploration wells were drilled in the arches of the largest and most elevated anticlinal structures. Initially, the main objects of search were terrigenous deposits of the Lower Oligocene and Lower Miocene. Crystalline basement formations were not considered promising. The structures of the Central Uplift, the Chatan monocline, the South Conson depression and the Priconson monocline were successively involved in exploratory drilling. This made it possible to reasonably evaluate the industrial potential of a significant part of the water area of ​​activity of the Vietsovpetro joint venture.

The first exploration wells produced various oil inflows and discovered the White Tiger (1984), Dragon (1985), Tamdao and Daihung (1988), Bavi and Baden (1989), Wolf (1990) fields. . In all fields, except for the Tamdao field, sediments of the Lower Oligocene and Lower Miocene turned out to be productive; In the Tam Dao field, minor oil flow was obtained from the basement.

In connection with the discovery of a unique deposit in the basement at the White Tiger field in 1988, the directions of search and exploration objectively changed.

The main discovery of the Vietsovpetro joint venture is the White Tiger field, large in reserves and unique in geological structure and oil and gas content. Approximately 70% of the initial geological reserves of categories C 1 + C 2 are concentrated here. It is characterized by a large volume of oil-saturated granitoids, a basement deposit height of at least 1,300 m, and a large accumulated production of anhydrous oil. Wells here were drilled to a depth of 5,014 m, but even at these levels no bottom water was found. The deposits of the Lower and Upper Oligocene and Lower Miocene are also productive. The White Tiger structure is a large horst-anticlinal uplift formed by northeast-trending longitudinal consedimentary faults. Their amplitude along the surface of the foundation reaches 1,500–1,600 m. The White Tiger deposit has already been quite well explored.

The Dragon deposit is located close to the White Tiger deposit and articulates with it en echelon. The field is confined to a complex structure and consists of two disconnected parts that do not have a common oil-bearing contour for any deposit. Conventionally, the Dragon deposit includes small local structures associated with uplifted basement blocks on the Prikonson monocline.

Despite the fact that the Dragon structure, like the White Tiger, is located within the Central Rise, their structure is significantly different - the Dragon structure is not a horst, there are no longitudinal breaks. The structure of the sedimentary strata at both deposits is approximately the same. The Dragon field has the same stratigraphic productivity range as the White Tiger field, but its reserves are significantly smaller. The main part of them is concentrated in the central area (boreholes 16–109) and is confined to Lower Miocene deposits. The deposits are complex bodies consisting of interbedded thin permeable sandy-siltstone and clayey layers. The foundation formations are water-bearing right up to the surface.

In the northeastern section (wells 3–7), industrial flows of oil and gas are obtained from deposits of the Lower Miocene, Upper and Lower Oligocene, and a minor influx of oil from basement formations where the oil reservoir is underlain by water.

The near-water part of the Dragon deposit has been fairly well explored, and its potential has been reliably assessed. The main prospects for searching for new deposits here are associated with Lower Oligocene deposits developed within the vast eastern wing of the structure. According to available geological and geophysical data, their thickness is much greater than in the areas studied by drilling. Numerous traps of non-anticlinal type are developed here, tectonically and lithologically screened, adjacent to the basement surface, under erosion surfaces (unconformities).

One or two wells were drilled in other local structures (blocks) of the Prikonson monocline. In the well 11 high-rate oil inflows were obtained from basement granitoids and Lower Oligocene sediments, in well. 14 – from basement formations; Lower Oligocene deposits in the arch of the structure are eroded.

The exploration of resources in general for the Vietsovpetro joint venture is quite high - reserves of category C 1 are 61.5%, and category C 3 - only 18.1%. Taking into account this indicator, as well as the limited area of ​​activity of the enterprise and the geological and geophysical information available on it, it can be stated that there is no basis for predicting the discovery of new deposits here with significant reserves. At the same time, the existing non-localized promising resources of category C 3 at the Dragon field allow us to hope for the discovery of several fields (deposits) - satellites, possibly profitable for development. The real basis for increasing industrial reserves are reserves of category C 2.

JV Vietsovpetro has developed a geological exploration program. It is determined by the actual results of geological exploration to study the oil content of individual areas and productive complexes of fields; the size and structure of undiscovered reserves and resources of categories C 2 and C 3; technical and economic capabilities of the enterprise. In accordance with these factors, two main directions of geological exploration work have been formulated.

1. Additional exploration of already discovered oil deposits and searches for new ones at the most promising objects (areas, blocks) of the Dragon field (area). To implement this direction, it is planned to drill several wells in the peripheral areas of the Dragon structure. This will make it possible to transfer at least 50% of category C 2 reserves and about 30% of category C 3 resources to category C 1.

2. Additional exploration of the Southern arch of the White Tiger deposit and the search for new deposits in Oligocene deposits and basement formations in its individual blocks. To implement it, it is planned to drill additional wells.

The implementation of this program will strengthen the resource base for oil production in the coming years. Providing a longer-term perspective for the activities of a joint venture requires fundamentally new solutions.

Concepts of the formation of unique deposits in granitoids

The initial geological reserves of the foundation deposit of the White Tiger field were previously estimated at 600 million tons, and the Oligocene deposits - 150 million tons, which in total amounts to more than 750 million tons of oil. Calculations showed that when the generation potential of Oligocene deposits was realized within the oil-gathering area around the White Tiger field, oil deposits could only form in the Oligocene complex itself.

The data obtained refute the established traditional ideas about the mechanism of formation of oil deposits in the basement of the White Tiger field only due to the resources of Oligocene sediments. Apparently, the granite foundation contains its own additional hydrocarbon sources for the accumulation of oil deposits in real parameters.

Many researchers note that the formation of hydrocarbon accumulations in the basement of platform areas could occur both due to the influx of hydrocarbons from adjacent sedimentary strata, and due to the basement’s own hydrocarbon potential. Most of the granitoids that make up the foundation of platform areas, as well as the entire “granite” layer of the earth’s crust, are not so much of igneous as of metamorphic origin. The formation of granite rocks could occur in subduction zones when an oceanic plate subsides under an island arc or under an active continental margin. The basaltic crust of the oceans, together with pelagic sediments, falls to significant depths with ever-increasing temperature and pressure. Under the influence of these factors, basement rocks and sedimentary cover gradually lose bound water, excess silica, alkalis, and lithophile elements. The process of dehydration of the oceanic crust occurs through a complex multi-stage reaction. The water released is water vapor, which has a very high alkaline reserve.

Thus, on the one hand, the hot water-mineral flow removes excess heat from subduction zones, and on the other hand, it saturates the lithosphere rocks with fluids rich in silica and alkalis. As a result, the earth's crust is enriched with oxides of potassium, sodium, aluminum, silicon and other compounds typical of the “granite” layer. As a result, this leads to granitization processes and the appearance of andesitic magmatism.

The mechanism of saturation of crystalline basement rocks with naphtide fluid is also closely linked to the proposed model of the genesis of granitoids. The primary sedimentary complexes (Jurassic, Cretaceous and Early Paleogene age), which participated in the processes of accretion, granitization and the formation of the “granite” crust of the Sunda shelf, also contained dispersed organic matter. The thermal water-mineral flow had a temperature and metasomatic effect on the overlying sedimentary strata. In this case, part of the organic matter (OM) was melted in submagmatic chambers, but its large mass could well have been preserved and become the basis for the formation of various types of naphtide-generating systems:

– hard carbon, anthraxolite-like accumulations;

– dispersed, sorbed, light;

– encapsulated gas-liquid hydrocarbons (C 2 – C 6), etc.

Thus, almost simultaneously with the formation of the “granite” layer of the Sunda shelf crust, hydrocarbon fluids also arise, which are included in the general water-mineral flow, with which they enter the sedimentary rocks of the island arc.

An important argument in favor of the proposed idea is the detection of hydrocarbon gases in bubbles encapsulated in granites of this region. Special studies carried out at VNIIgeoinformsystems identified and analyzed gas-liquid fluids that form inclusions in foundation samples of the White Tiger and Dragon fields. Only fluids from closed voids were isolated and analyzed, which could only be obtained by mechanical destruction of the sample under high vacuum conditions. These fluids are encapsulated in capillaries, mineral growth channels, and voids of specific mineral structures in the form of separate inclusions (vacuoles).

The inclusions contain a relatively high content of hydrocarbon gases C 2 – C 6 and higher. Thus, in granite lifted from a depth of 4584.1 m (well 442 White Tiger), the content of C 4 H 10 reached 11.6 cm 3 /kg, C 5 H 12 - 11.2, C 6 H 14 - 11, 9 cm 3 /kg of breed. This indicates, according to Moscow researchers, that the primary source of hydrocarbons could be sedimentary rocks, both those that participated in recrystallization and granitization, and those that were drawn into subduction zones. A kind of water-mineral flow arose, saturated with hydrocarbon gases. The latter could be captured and encapsulated in the vacuoles of granitized rocks.

If we assume that the average content of hydrocarbon gases is 15 cm 3 /kg, then in the 10-kilometer “granite” layer of the crust of the Cuu Long depression alone, with an area of ​​20 thousand km 2, about 10 trillion m 3 of hydrocarbon gases, mainly methane, are contained in dispersed form.

The participation of hydrocarbon fluid in the “gas breathing” of the earth’s interior and, as a consequence, the encapsulation of hydrocarbon gases in the form of inclusions in microcracks of rocks and foundation minerals, has been noted by a number of researchers for other regions of ancient and young platforms.

As a result of the movement of hydrocarbon flow from bottom to top, a clearly defined vertical zoning in the distribution of oils is observed in the White Tiger field: light oils in the basement and lower Oligocene sediments, heavier oils in the upper Oligocene and lower Miocene rocks. This zoning is explained by the fact that the process of oil formation occurs in the basement at the present time. The arrival of new, fresh portions “dilutes” the oil, making it relatively light, while oils of the Upper Oligocene - Lower Miocene located higher up the section, not associated with this source, have lost part of their light fractions.

Summarizing the above arguments, we can suggest that during the period of formation of the “granite” layer, due to the granitization of primary sedimentary strata, the process of transformation of dispersed OM into hydrocarbons of the oil series took place. Under severe thermobaric conditions, light hydrocarbon fractions were generated, which formed the basis of the oil deposit in the basement of the White Tiger and Dragon fields. In addition, hydrocarbon fluids rising from underthrust zones along with the water-mineral flow settled in igneous and sedimentary rocks when thermobaric conditions changed. Through cracks and other channels, liquid hydrocarbons from the basement could penetrate into the Lower Oligocene deposits.

If we accept the stated idea about the formation of oil in the basement rocks of the Sunda shelf, then the potential oil resources of the White Tiger field will increase significantly. In addition, the proposed mechanism of oil and gas formation can be extended to neighboring structures located in the area of ​​action of rifts or thrust zones and having geological conditions similar to the White Tiger field.

As already mentioned, in 1988, the unique White Tiger oil field was discovered in the fractured granitoids of the Mesozoic basement of the Cuu Long Basin. It has a proven thickness of more than 1,600 m and a volume of oil-saturated granitoids of 88.2 billion m 3. This discovery intensified exploration work on the formations of the magmatic basement on the shelf of Vietnam and in the region as a whole, and in other areas of the world.

Despite the presence in the world of several hundred deposits confined to igneous and metamorphic basement rocks, the White Tiger deposit is unique both in terms of reserves and production levels. Over 13 years of exploration and development of oil deposits in the foundation of the field, about 100 million tons have already been produced.

The Mekong oil and gas basin (especially the Cuu Long Basin) is the first area on the Vietnamese shelf where powerful oil gushers were produced from fractured granitoid basement ledges. At the White Tiger field, an oil gush with a flow rate of about 2,830 t/day was obtained from a depth of 3,150 m.

Let us recall that the foundation of the White Tiger is a large horst-anticlinal uplift of a complex structure, measuring 22×9 km. It consists of three vaults - Southern, Central and Northern. The structure is broken by a series of faults, mainly of submeridional strike and subordinate sublatitudinal faults. Currently, more than 120 exploration, production and injection wells have been drilled into the foundation, which provide more than 90% of the total oil production in the field (Fig. 2).

Rice. 2. Geological profile of the Vietnam shelf (Areshev, 2003):
1 – geological profile of the Vietnamese shelf, illustrating the granitoid projections of the basement; 2 – schematic profile of the White Tiger deposit

Most of the wells on the White Tiger drilled on the foundation are high-yield (yields more than 1,000 tons/day). The exposed thickness of the igneous basement rocks reaches 2,000 m. The lower boundary of the deposit is conditionally established to an absolute depth of 5,014 m. Oil-bearing reservoirs are fractured-cavernous reservoirs, the voids of which are represented by macro- and micro-cracks, isometric caverns and matrix voids. The uniqueness of the White Tiger field lies, first of all, in the large thickness of the productive section, in which oil-bearing rocks are primarily young Late Cretaceous granitoids.

In terms of mineral composition, the section of the White Tiger intrusive massif is represented by granites, granodiorites, quartz diorites, monzodiorites, amphibole leucodiorites (diorites), the transition between which is not always clear enough. In addition, the massif is cut by numerous dikes of comagmatic Oligocene volcanic rocks, represented by diabases, basalts, and trachybasaltic porphyrites, forming lava covers above the basement.

It seems possible to generalize these phenomena using mathematical models. The main problem that arises along this path is that these fluid processes are multifactorial and multiparametric. Among them, it is difficult to single out just one dominant factor that can be simplified and schematized.

Edition: Moscow, 2010, 10 pages, UDC: 550.8.02

Language(s) Russian

The work is devoted to the analysis of fracture systems (fractures and faults) developed in the basement rocks and sedimentary cover at the White Tiger field. By fracture systems we mean the entire set of rock discontinuities of different ranks (from microcracks to faults), recorded by various research methods and having a different scale, but typical for a particular research method. The objective of the research was to differentiate the entire variety of fracture systems developed in the basement rocks of the White Tiger field, based on their permeability for filtration of fluids during the exploitation of the deposit. A graphical illustration of the analysis results allows us to visualize the patterns of distribution of fracture systems in the sedimentary cover and in the basement of the White Tiger field.

Publication: FSUE VNIGRI, Moscow, 2012, 17 pages, UDC: 552.578.061.43:552.3, ISBN: 2070-5379

Language(s) Russian

Information is presented on the industrial oil content of unconventional objects and the concentration of hydrocarbons in granitoid reservoirs. The geological characteristics of the world's steepest deposits are given. Particular attention is paid to the description of the oil content of the Vietnamese shelf, where uniquely productive fields have been discovered. A critical assessment of the results of geological exploration work on the foundation in Tataria is given.

The industrial oil and gas potential of the foundation of platform areas is one of the actively discussed problems in modern oil and gas geology. The discussion was intensified by the discovery in 1988 of a unique oil deposit in the granites of the Mesozoic basement of the southern Vietnam shelf in the White Tiger field.

However, this problem arose earlier. It dates back to the receipt of an industrial influx of oil and gas from fractured granites in the Panhandle-Hugoton field (USA) in December 1918. In 1925, in the giant oil field of La Paz (Venezuela), more one oil deposit in the basement.

Currently, more than 450 fields with industrial accumulations of oil, gas and condensate are known in the basement of 54 oil and gas basins of the world [Gavrilov. Gulev. Knreev. 2010].

Brief characteristics of oil fields in granitoid rocks

Accumulations of oil and gas in igneous and metamorphic basement rocks and weathering crusts have been discovered on almost all continents and in the World Ocean. However, despite the discovery of industrial deposits in the basement, including large ones, targeted searches for hydrocarbon deposits in the basement, especially in igneous rocks, are carried out in limited quantities. This is due to this. that the nature of the capacity of the basement rocks is not clear, methods for identifying reservoirs in crystalline rocks, their opening and development have not been developed.

Edition: Tomsk Polytechnic University, Tomsk, 2012, 4 pages, UDC: 550.84:551.8

Language(s) Russian

The White Tiger (Bach Ho) field is located on the southern shelf of the SR Vietnam in block 09–1, 120 km southeast of the port city of Vung Tau, the main production, technical and supply base of the Vietsovpetro joint venture (Fig. 1). Oil deposits were found in Lower Miocene and Oligocene sandy-siltstone deposits, and also, contrary to preliminary expectations, in fractured granitoid reservoirs of the basement. The rare case of discovering industrial accumulations of oil in crystalline rocks attracts special attention. The White Tiger field has become the largest field in the oil-bearing province, confined to the central uplift of the Cuu Long Basin.

To restore the history of the formation of hydrocarbon accumulations in the Earth's interior and reconstruct the conditions of naphthiogenesis, a detailed study of the composition of organic matter dispersed in rocks is necessary, in particular the distribution of chemofossils in it, which inherited the features of their structure from biological predecessors. The composition of these structures is determined, first of all, by the initial biomass and the subsequent stages of its transformation.

The complex of chemofossils (the individual composition of isoprenoid and normal alkanes, the content of metalloporphyrins and perylene), as well as the composition of phenathrenes, which we selected for research, allow us to judge the facial-genetic nature of the organic matter present in the rocks. Thus, the presence of complexes of porphyrins with vanadyl (VO-p) in organic matter indicates the predominantly marine genesis of organic matter and reducing conditions during sedimentation. The presence of nickel porphyrins (Ni-p) indicates the absence of hydrogen sulfide contamination of natural waters during sedimentation and early diagenesis of organic matter. Prilene, widespread in lakes, is also found in coastal areas of the seas and is absent in deep-sea facies. Isoprenoid hydrocarbon ratio

pristane (P) and fritan (F) can be used to assess the redox conditions in the sedimentation basin. It should, however, be taken into account that, along with the oxidizing environment, the increased content of pristane in sediments may be due to a significant contribution of zooplankton and bacterial biomass in organic matter. The composition of n-alkanes characterizes the participation of certain groups of bioproducers in the formation of the composition of organic matter. The main hydrocarbons of phytoplankton are C15 and C17 n-alkanes. Terrestrial vegetation is characterized by the predominance of C27, C29 and C31 n-alkanes. Coastal seaweeds are dominated by C21, C23 and C25 homologues.<...>

In recent years, the relevance of studying these issues has increased significantly throughout the world, both in connection with the discovery of new large oil and gas fields in the basement, and with the gradual depletion of hydrocarbon (HC) reserves in fields with terrigenous and carbonate rocks.

In the Republic of Vietnam, the share of oil production from the basement deposits of the White Tiger, Dragon, Black Lion and other fields exceeds 90% of total oil production. Therefore, the study of issues of control and regulation of the development of these fields becomes more relevant and indeed has great practical importance in oil and gas field practice.

Oil deposits in the basement are often determined by complex geological and thermodynamic conditions. Consequently, the analysis and regulation of the development of fields with such conditions are not only of scientific interest, but also of extremely great practical importance both for the Republic of Vietnam and for the whole world. The dissertation work analyzed and regulated the development of granitoid reservoirs in the crystalline basement of the large White Tiger field on the shelf of South Vietnam.