Characteristics and Origin of Overpressure in the Northwest Part of Nanpu Sag

Abstract

Abstract

Nanpu sag is a hydrocarbon generating sag developed in the Meso-Cenozoic in the Bohai Bay Basin. Under the guidance of petroleum geology, logging geology, overpressure response and calculation model method and technology, this paper is mainly to study nowadays pressure characteristics of Sh-ahejie Formation and Dongying Formation in the northwest region of Nanpu Sag based on structural evolution, burial history of sedimentary basin. According to acoustic time method and all kinds of analysis and test datanabout geol-ogy, drilling and well logging, we identify the pressure structure of single well and profile, then build relations-hips with pressure and a variety of compaction curves to predict the formation fluid pressure by the method of Eaton.

The study shows that: (1) Based on a large number of drill stem test (DET) data, the burial depths of overpressured sandstone reservoirs range from 3000m and 4900m with pressure coefficients of 1.206 to 1.77(2)There are three structural styles of abnormal pressure of the northwest region of Nanpu, respectively single overpressure structure, double overpressure structure and normal pressure structure(3) In the northwest region of Nanpu sag, overpressure appears from the second member of Dongying Formation (Ed2), but the first member of Dongying Formation (Ed1) and formations above it are not found overpressure(4)The double overpressure system in vertical structure, presenting as four stages or more stages in the pressure profile diagram, has the obvious 4-pressure-structure layer in the northwest region of Nanpu sag, that is normal pressure to overpressure to weak overpressure or normal pressure to overpressure from up to down(5)The abnormal overpressure in the study area is caused by undercompaction.

Key Words: character of overpressure; acoustic time; origin of overpressure; pressure prediction

AAPG Datapages/Search and Discovery Article #90260 © 2016 AAPG/SEG International Conference & Exhibition, Cancun, Mexico, September 6-9, 2016