Study On Sand Bodies Distribution Of The 8Th Member Of Xiashihezi Formation And The 1St Member Of Shanxi Formation At Su-14、Tao-7 In The Centre Of Sulige Area

Erdos basin is the second largest sedimentary basin of China. The total area accounts for 4% of the land area. In recent years, Shanbei slop is the main exploration and development region. Sulige Gas Field which has been found is in the northern of Shanbei slop. Its gas-bearing layers are Carboniferous and Permian. The 8th member of Lower Shihezias is one of the main production layers in this area. This work area is located in Su 14, Tao 7 blocks of Central Erdos basin, with the total area of 1.3×103km2. Fine stratigraphic division and correlation of Tao 7, Su 14 blocks is the basic work of all oil and gas reservoirs. To divide and contrast the formation reasonably is an important program from single well to multi-well evaluation in oil and gas reservoir description. It is the premise to describe the reservoir pattern and spatial distribution characteristics and change rules of reservoir parameters. It is also of great significance for the fine development of oil and gas fields.As the largest monolithic gas field onshore, many research institutions have done a lot of research on its main gas producing layer--the 8th member of Lower Shihezi and the 1st member of Shanxi formation. In recent years, exploration and development work have been carried out in Sulige area; therefore there are many complex problems to face. Sulige gas field is mainly controlled by the formation of the upper Paleozoic River, delta sand body distribution and basin tectonic background. Sulige gas developed large sandstone lithologic traps. The main gas reservoir is the 1st member of Shanxi formation and the 8th member of Lower Shihezi formation. From the proof of many years’ exploration and development of production practice, the 8th member of Lower Shihezi formation is much thicker than the 1st member of Shanxi formation with high reservoir heterogeneity. Aiming at the geological problem of sedimentary environment and reservoir, Research Institute of Changqing oil field as well as many colleges and research units have carried out a lot of research and exploration work, but understanding of the various aspects are still inconsistent.This paper focuses on the 1 st member of Shanxi formation and the 8th member of Lower Shihezi formation. Combined with the results of previous studies, using the observation and study of logging data, this paper finds that main problems existing in the central region are that stratigraphic division is not clear enough and the sign layer characteristics and influence factors of sand body distribution and microscopic characteristics are not obvious. The overall thickness of sandstone is stable and sand body distribution in the transverse direction is complex and in the vertical direction lithologic difference is large in the 1st member of Shanxi formation and the 8th member of Lower Shihezi formation. Also effective sand body connectivity is poor and single well production is low. There are many well drillings in Tao 7, Su 14 blocks, but they do not have unified stratum and reservoir mapping so that the overall distribution characteristics of the reservoir is not clear of the 1st member of Shanxi formation and the 8th member of Lower Shihezi formation in these two blocks. It is necessary to study the strata and sand body distribution etc. in these two layers so that it can provide proof for the next steps’exploration and deployment.Based on geological and logging data of hundreds of oil and gas wells and compared with the popular division plan, the research center of Sulige carries out systematic comparative study of stratigraphic division about Carboniferous and Permian. It is the base and key of fine reservoir description to carry out accurate stratigraphic classification, comparison and stratigraphic framework establishment. This paper uses the lithostratigraphic division to divide Upper Paleozoic into Benxi Formation, Taiyuan Formation of Permian, Shanxi, Shihezi formation and Shiqianfeng Formation from bottom to top in Sulige gas field. The total thickness of sedimentary rocks is about 700m. The main gas-bearing layer is located in the 1 st member of Shanxi formation and the 8th member of Lower Shihezi formation, both of which were developed continually with the thickness of about 90-100m and burial depth of about 3200-3500m. They are shallow in the northeast and deep in the southwest. Combined with the use of large amounts of log data and sign layer, this paper carries out a detailed classification and correlation of the 8th member of Lower Shihezi and the 1st member of Shanxi formation and get a clear understanding about the distribution of strata. The sand body of the 8th member of Lower Shihezi and the 1st member of Shanxi formation distribute nearly north-south and its thickness gets more thick from the south to the north. The sand bodies of these two formations show a contiguous channel and folds northward overall. The 1st member of Shanxi formation has been divided into 6 sets and the 8th member of the upper and lower Shihezi formation have both been divided into 4 sets. And the sand body of the 1 st member of Shanxi formation presents banded distribution, and the sand body of the 8th member of Lower Shihezi formation presented braided distribution. Based on clear stratigraphic correlation, this paper analyses the effectiveness of sand body distribution and the contiguous distribution characteristic of reservoir in North-South and East-West. The effective sand body and gas distribution is relatively obvious in the work area. The gas content and connectivity is the best in the lower 8th member and it is relatively poor in the upper 1st member of Shanxi formation and the upper 8th member. But overall the contiguous sand bodies are relatively small with multi-period development in Su 14, Tao 7 blocks with a lot of wells. And effective sand body connectivity is limited.This paper discusses the formation of large layers which have relatively obvious sign layer and their thickness variations are also relatively stable. Based on the relative stability of the stratigraphic thickness, this paper carries out analysis and research work about vertical and horizontal distribution characteristic of reservoir sand and sand body and draws up sand body distribution and effective sand distribution map and gas reservoir profile map. Then it further clarifies the distribution of sand body of the 1 st member of Shanxi formation and the 8th member of Lower Shihezi formation in Su 14, Tao 7 blocks of Central Erdos basin. It has a positive significance for looking for more quality reservoir and accelerating natural gas exploration and development stage.