鄂尔多斯盆地靖边气田前石炭纪古地貌解释新模式

A new interpretation mode for pre-Carboniferous paleo-geomorphology of the Jingbian Gas Field, Ordos Basin

近年来,鄂尔多斯盆地靖边气田在原有古地貌解释模式下部署的多口勘探开发井钻探均告失利,二维地震储层预测准确率下滑至70%以下,制约了该区天然气勘探的进程。为此,在综合分析已有古地貌恢复方法优缺点的基础上,根据印模法、残余厚度法的基本原理,结合钻井、测井资料,创建了一种考虑古构造影响的定量古地貌恢复方法,并利用该方法对该气田进行古地貌恢复与侵蚀沟槽重新解释。研究结果表明:(1)该区下古生界储层沟槽解释模式由原来的"东西向大型侵蚀沟槽、南北向毛细沟槽模式"修正为"东西侵蚀主沟槽与局部侵蚀潜坑并存"新模式;(2)较之于原预测结果,下古生界侵蚀主沟槽东西向长度缩短近1/2,毛细沟槽发育范围较小,局部被半径介于1~15 km的潜坑替代;(3)据重新解释的成果,该区下古生界气藏可扩大含气面积305 km^2,预计可建天然气产能4.5×10~8 m^3/a。2016—2017年,利用该研究成果在原解释的沟槽内部署井位30口,目前已完钻8口井,7口井下古生界奥陶系马家沟组马五1+2亚段储层保存完整,其中5口井试气的平均无阻流量为14.3×104 m^3/d,证实新方法能准确地对该区古地貌进行定量化表征、提高储层预测的准确率。

In recent years, due to the existing interpretation methods of paleo-geomorphology, many exploration and development wells deployed in the Jingbian Gas Field, Ordos Basin witnessed failures. Besides, the accuracy of 2D seismic reservoir prediction dropped to below 70%. Consequently, the natural gas exploration in this area is restricted. In this paper, both advantages and disadvantages of the existing paleo-geomorphology restoration methods were analyzed comprehensively. Then, a quantitative paleo-geomorphology restoration method considering the influence of paleo-structure was developed according to the basic principles of impression method and residual thickness method, combined with the drilling and logging data. This method was applied to paleo-geomorphology restoration and erosion groove reinterpretation in the Jingbian Gas Field. The following results were obtained. First, the groove interpretation mode for the Lower Paleozoic reservoirs in this area is modified from the previous mode of ＂east-west large erosion grooves and north-south capillary grooves＂ into the new one of ＂coexistence of east-west erosion grooves and local erosion pits＂. Second, compared with the results predicted by the existing methods, the proposed method reveals that the main erosion grooves of Lower Paleozoic is 1/2 shorter in the direction of east-west and the development area capillary grooves is smaller and locally replaced by pits of radius of 1-15 kin. Third, the reinterpretation results indicate that the gas-bearing area of Lower Paleozoic gas reservoirs in the Jingbian Gas Field can be increased by 305 km2, where it is expected that an annual gas productivity of 4.5× 10^8 m^3 can be constructed. Based on these results, 30 wells were deployed in the originally interpreted grooves during the period from 2016 to 2017. So far, 8 wells have been drilled, among which the Ordovician Ma51＋2 gas reservoirs are well preserved in 7 wells, and an average absolute open hole flow of 14.3×10^4 m^3/d is realized in 5 wells. It is demonstrated that the new method can quantitatively characterize the paleo-geomorphology accurately and increase the reservoir prediction accuracy.