Assessment on gas accumulation potential and favorable plays within the Xu-1, 3 and 5 Members of the Xujiahe Formation in the Sichuan Basin

Natural gas exploration and discovery of hydrocarbons in the Xujiahe Formation in the Sichuan Basin are mainly concentrated in the Xu-2, 4 and 6 Members. The discovered gas reservoirs are characterized by a low filling degree, high water saturation in lower intervals, low levels of produced reserves and a limited number of gas-bearing reservoirs. The Xu-1, 3 and 5 Members are identified as source rocks. Based on the study of natural gas accumulations and several gas production wells in the Xu-1, 3 and 5 Members, this paper proposes that large scale sand bodies are developed in the Xu-1, 3 and 5 Members in the northwest, southwest and central parts of the Sichuan Basin. In each member, the favorable gas bearing area is about 5 000-11 000 km2, the reservoir rocks have good continuity with single layer extensions of up to 15-20 km. It is believed that these sand bodies have favorable conditions for gas accumulation within source kitchens to form lithologic or structural-lithologic gas reservoirs and have better accumulation potential and higher gas-bearing abundance than that of the Xu-2, 4 and 6 Members. Exploration practices have revealed that economic gas reserves may be generated. It is suggested that more efforts be made to study the gas accumulation conditions in the Xu-1, 3 and 5 Members (especially the Xu-3 and Xu-5 Members) and more exploration work be conducted in these strata.

摘要：目前四川盆地须家河组天然气藏勘探和发现主要集中于须二、四、六段，气藏总体表现出充满度不高、低部位含水饱和度偏高、储量动用比例偏低、储集层含气范围有限的特点，须一、三、五段则被作为烃源岩。在对须一、三、五段进行成藏条件研究和已知出气点解剖分析的基础上，提出川西北、川西南和川中部分地区须一、三、五段发育规模较大的砂体，各段有利含气面积约5 000～11 000 km2，储集层连续性较好，单层延伸长度达15～20 km，具备源内成藏的有利条件，可形成岩性或构造-岩性圈闭气藏，比须二、四、六段的成藏潜力和丰度更好，经勘探可形成工业规模的天然气储量，今后应该加强上述地区须一、三、五段源内天然气成藏研究与勘探力度，尤其是须三和须五段。图8表4参19