Link for citation: Nguyen Xuan Kha, Pham Xuan Son, Hoang Van Quy, Nguyen Tuan, Truong Quoc Thanh, Mai Huu Xuan, Tran Van Xuan.  Bach ho field geological features identification using  well logging data. Bulletin of the Tomsk Polytechnic University. Geo Аssets Engineering, 2023, vol. 334, no. 7, рр. 35-42. In Rus. The relevance. Well geophysics is considered as a typical method that can assist in determining the petrophysics properties of reservoirs and further location of the petroleum product-containing reservoirs. For reservoirs formed from fractured basement rock, studies on the petrophysics properties of fracture zones can contribute to the identification of petroleum products. The main aim. The study applied the cross-plotting method based on raw well-logging data to identify the possible correlation between the gamma-ray logging with well-logging including neutron porosity, sonic transient time, and bulk density in three wells (BH-433, BH-809, and BH-905) of Bach Ho field in the Cuu Long Basin, Vietnam. Methods. To deploy this study, well-logging data were integrated into formation of micro images and neutro, speed of sound, and density of the basement at the surveyed reservoir positions. Results. The results indicated that granite in the investigated zones responds to the two tight value ranges (no-oil exist zones) neutro (0,000–0,100) and speed of sound (46–64), and neutro (0,000–0,100) and density (2,375–2,750) while the value ranges deviate from 0,000–0,100, 46–64, and 2,375–2,750, respectively for neutro, speed of sound, and density are closely related to the good permeability and porosity zones (oil exist zones). Based on the findings, it can be confirmed that the cross-plotting analysis has contributed positively to the initial assessment of potential ranges of the oil reservoirs in Bach Ho field. The application of the cross-plotting method will contribute to enhancing the predictability of oil and gas in the reservoirs.

During the 40 years of operation and development (1981 - 2021), the Vietnam - Russia Joint Venture "Vietsovpetro" has witnessed many historical milestones, but the discovery of industrial oil for the first time from the fractured and weathered granite basement at exploration well BH-6 on 11 May 1987 is the most important one. From the first oil in the basement rock of Bach Ho field, Vietsovpetro consecutively discovered industrial oil in other fields in its area of operation, such as Dong Bac Rong (1991), Dong Nam Rong (1995), Nam Rong (2005), Nam Trung Tam Rong (2006), etc. At the beginning of 2018, the 2P (P1+P2) oil reserve from the basement rock accounted for 74% of Vietsovpetro's total balanced reserves at that time. As of 1 October 2021, the total oil produced from the basement reached 235 million m3 (195 million tons), accounting for 86% of Vietsovpetro's total oil output. Being encouraged by the success and experience of Vietsovpetro, other domestic and foreign oil and gas companies (PVEP, JVPC, Talisman, and Petronas, etc.) have explored and discovered oil and gas from the granite basement and put the fields of Rang Dong, Su Tu Den, Hong Ngoc, and Hai Su Den, etc. into operation. This fact has, at the same time, created a strong attraction for domestic and foreign investors, making important contributions to the rapid development of Vietnam's oil and gas industry which was still very young at the time. The above-mentioned shows that it is time to study data and documents, draw lessons from success and failure gained during the 40 years of basement exploration. The outcomes should be used as a basis to formulate an appropriate exploration strategy for Vietsovpetro in the coming decades with strong fluctuations in the oil and gas market expected, and the inevitable depletion of non-renewable resources worldwide.