Prediction For Carbonate Reservoirs At Leijia Area Of Liaohe Depression

Located in the northwestern part of Chenjia depression, Leijia-Gaosheng carbonate rock zone is an area with complex lithology and it mainly includes thin-interbedded rocks such as argillaceous dolomites, cloud mudstone and grained dolomites which lay on the surface of the basalt of the Mesozoic group. Volcanic breccia is mainly from Chenjia depression and Chenjia footwall. Due to the multi-phase fault activities and the basement tectonic activities, the cracks developed among the argillaceous dolomites, cloud mudstone and volcanic breccia, which formed a good hydrocarbon pore volume close to Chenjia depression. After many years’ exploration, it has been confirmed that Chenjia depression is a good place to supply oil and gas since this area has rich oil resource. Leijia is located in the west sag of Liaohe depression with a lower exploration degree. The present investigation would focus on the special lithologies such as carbonate rocks in the 4th member of Shahejie formation.In the present research, the author tries to explore the dominating factors controlling hydrocarbon accumulation of special reservoir such as carbonate rocks, volcanic breccia, etc. around Chenjia depression by making an analysis of the distribution characteristics of special reservoir in Chenjia depression, the crack formation mechanism, reservoir forming conditions and reservoir modeling so as to expand the exploration area and exploration scale.With a higher degree of exploration and improvement of developing methods, good oil and gas was discovered in the 4th member of Shahejie formation in the exploratory wells within this area from 2008 until now. Since further studies have been made on the seven properties of the tight oil, all the wells that finished drilling obtained high yield flow of industrial oil at the beginning of 2013, which displayed higher value and great potential of tight oil exploration in the Leijia area.At present, tight oil exploration is a key research project and in 2013, within the Liaohe oilfield the carbonate rocks in the 4th member of Shahejie formation were targeted for tight oil study so as to gain further information and enhance technical reserves. The present project aims to deal with key tight oil problems, seismic prediction techniques, distribution of the most favorable reservoir zones as well as technical supports. There are new achievements being made and through a new technology relationship, the whole project was successfully completed. All the new understandings, developments and breakthroughs achieved from the present research could further enrich and improve the matched technology adopted in the study of carbonate tight oil reservoir in the Leijia-Gaosheng area. It could also improve work efficiency and provide better guidance for the exploration work and researches of tight oil reservoir in the present area as well as those in the whole Liaohe depression.Leijia area is on the western slope with Chenjia depression on the east and the cracks are predicted to be developed in nearly east-west direction and north-east direction. In the early times, the fault in the north-east direction was cut into many fault blocks by the fault in the nearly east-west direction. This region is near Chenjia oil-depression which was a good oil source. As early as 1990s, many carbonate oil and gas reservoirs were discovered in this region, however, no further breakthrough was made in recent years. For this region, the major reservoir lithology includes shallow lacustrine dolomites, argillaceous dolomites, dolomite mudstone in the 4th member of Shahejie formation and the fine-grained dolomites in the Gaosheng area, and under the force of multi-phase fault activities with multiple properties and under the force of weathering and leaching, those lithologies became good reservoirs. According to the research, it is found that there is good hydrocarbon accumulation in this region and it has great exploration potential. However, the shale content in the carbonate rocks is a little high and there is a lower degree of porosity and permeability, which makes it a little hard to identify reservoirs with the information available.The carbonate reservoir in Leijia is mainly reservoir containing shallow lacustrine dolomites in the 4th member of Shahejie formation and this reservoir is characterized by a decreasing trend of layers with Leijia in the center. There is a variety of hydrocarbon accumulation including structural reservoir, structural and lithologic reservoir as well as lithologic reservoir.Though the author could get some guidance and reference for the present study from the results and understanding of previous researches on carbonate rocks in Leijia, the distribution of carbonate rocks still need to be further studied as the lithology and structural feature in the present region is a little complicated and the lateral distribution in the 4th member of Shahejie formation varies greatly. Under this situation, the author decided to do the present research. By conducting researches on sedimentology and reservoir prediction, the author tries to find new traps, to make new achievements in lithology exploration and promote hydrocarbon accumulation study so that it could open up a prospect for the exploration work in this region.