柴达木盆地冷湖地区第三系泥岩盖层封盖能力定量评价

Quantitative Evaluation of Sealing Capacity of Tertiary Mudstone Caprock in Lenghu Area, Qaidam Basin

柴达木盆地北缘第三系泥岩发育程度好且横向分布稳定,封气性能较强,是油气的主要区域盖层.根据钻井、测井和实测突破压力等数据,研究了柴北缘冷湖地区第三系泥岩盖层宏观发育特征及微观封闭机理;进一步选取盖层累计厚度、成岩阶段、突破压力、超压系数和脆性指数等为评价参数,对泥岩盖层封盖性进行了定量评价.结果表明:冷湖地区第三系发育路乐河组、下干柴沟组和上干柴沟组等多套泥岩盖层;泥岩盖层成岩阶段处于早成岩阶段A期至中成岩阶段B期;泥岩盖层突破压力达到1.1 MPa具有封盖工业油流的能力,达到2 MPa具有封盖工业气流的能力;总体上,下干柴沟组上段和路乐河组盖层封闭性最好,下干柴沟组下段次之,上干柴沟组相对最差.封闭性评价结果与勘探实践相匹配.

The Tertiary mudstone in the northern margin of Qaidam basin is the main regional caprock of oil and gas, characterized by lateral distribution stability and strong sealing ability. According to drilling, logging and breakthrough pressure data, the macroscopic development characteristics and microscopic sealing mechanism of the Tertiary mudstone caprock in Lenghu area of northern Qaidam basin were studied. Furthermore, the mudstone thickness, diagenetic stage, breakthrough pressure, overpressure coefficient and brittleness index are selected as evaluation parameters to quantitatively evaluate the sealing capacity of mudstone caprock. The results show that there is a series of mudstone caprock developed, such as Lulehe, Xiaganchaigou and Shangganchaigou Formations. Mudstone caprock diagenesis is in the early diagenetic stage A to the middle diagenetic stage B. The breakthrough pressure of mudstone caprock reaches 1.1 MPa, which has the ability of sealing commercial oil flow, and reaches 2 MPa, which has the ability to seal commercial gas flow. In general, the sealing ability of the upper member of Xiaganchaigou Formation and Lulehe Formation caprock is the best and the lower member of Xiaganchaigou Formation is relatively weak. The sealing ability of Shangganchaigou Formation is the worst. The results of sealing evaluation match with the exploration practice.