渤海湾盆地惠民凹陷临南洼陷沙河街组现今超压分布特征及成因

临南洼陷是渤海湾盆地济阳坳陷惠民凹陷中的主要富烃洼陷，油气田主要分布在洼陷内及其南北两侧的断裂构造带，临南洼陷深部沙河街组超压较发育。利用钻井、钻杆测压（DST）、测井和地震资料，结合Eaton超压预测经验公式，对砂岩实测压力特征、超压测井响应、超压剖面和平面分布特征以及成因进行了研究。临南洼陷沙河街组砂岩DST实测超压深度约为3 005~4 355 m，剩余压力约为7.95~30.45 MPa，压力系数约为1.21~1.78；超压带内的泥岩和砂岩均表现为偏离正常趋势的高声波时差响应特征，并对应泥岩高电阻率异常；层位上沙四上亚段至沙三中、下亚段地层主要发育弱超压，局部出现中—强超压；剖面上深洼区超压带分布的深度范围约在3 000~4 500 m；平面上发育多个小的中—强超压区，超压区主要分布在深洼区和中央断裂带范围，超压顶界面深度约为2 500~3 700 m。临南洼陷古近系砂岩占比高是超压发育比较局限的主要控制因素。该凹陷超压砂岩储层主要为含油层，含烃流体充注为临南洼陷深层沙三、四段砂岩超压的主要原因；优质烃源岩埋深大，超压烃源岩镜质体反射率约为0.5%~1.5%，处于生油阶段且不具有低密度特征，表明生油作用是烃源岩增压的主要因素。 

Distribution and causes of present-day overpressure of Shahejie Formation in Linnan Subsag,Huimin Sag,Bohai Bay Basin

The Linnan Subsag is a main hydrocarbon generating area in the Huimin Sag of the Jiyang Depression, Bohai Bay Basin. Oilfields mainly are in the subsag or on the southern and northern faults. Overpressure is found in the Shahejie Formation. Drilling, drill stem test (DST), logging and seismic data as well as the Eaton formula were applied to study the measured pressure characteristics in sandstones, the correspondence between logging and overpressure in both sandstones and shales, and the plane and profile distributions and causes of overpressure. The overpressure depth from DST ranges 3 005 to 4 355 m in sandstones of the Shahejie Formation, the residual pressure is 7.95 to 30.45 MPa, and the pressure coefficient is 1.21 to 1.78. Logged acoustic velocity of shale and sandstone in the overpressure zone is higher than that in the normal pressure zone, and the logged resistance of the overpressure zone is also higher than that of the normal pressure zone. The upper section of the fourth member and the middle and lower sections of the third member of Shahejie Formation mainly develop low overpressure, while medium and strong overpressure also exist regionally. Vertically, overpressure zones mainly occur from 3 000 to 4 500 m depth. There are several medium and strong overpressure zones, mainly in the deep sag and fault zone. The top depth of overpre-ssure zone is 2 500-3 700 m. The high percentage of sandstone leads to the limited distribution of overpressure in the Linnan Subsag. The overpressured sandstone reservoirs in this sag are mainly oil-bearing layers. Hydrocarbon-bearingfluid charging is the main reason for the overpressure of sandstones in the third and fourth members of Shahejie Formation in the Linnan Subsag. The high-quality source rocks are deeply buried. The vitrinite reflectance of the overpressured source rocks is about 0.5% to 1.5%. It is in the oil generation stage and does not have low density characteristics, indicating that oil generation is the main reason for the pressurization of source rocks.