The Characteristics of Fluid Potential Field and Hydrocarbon Migration in Deep Formations of Qikou Sag, Huanghua Depression, China

Wang, Deqiang ^1
1 University of Houston, Houston, TX.

The Tertiary formations below 3500m deep in Qikou Sag, Huanghua Depression, China, are very important hydrocarbon-bearing zones. The sandbody shows great variety in types and severely separated distribution. The high quality reservoirs are mainly controlled by vertical abnormal pressure. Understanding the characteristics of abnormal pressure distribution will help to build more accurate paleo-fluid potential fields. Since the fluid potential distribution is the control factor for hydrocarbon secondary migration and accumulation, an accurate paleo-potential distribution model will provide better prediction of the potential prospects.

In order to predict the prospects of deep formations in Qikou Sag, this paper rebuilt the evolution history of fluid potential fields for four formations, namely E_s3, E_s2, E_s1³ and E_s1²⁺¹, using basin modeling techniques. The primary processes in paleo-fluid potential reconstruction include paleo-pressure restoration, erosion thickness reconstruction, paleo-porosity calculation and burial history modeling. To obtain more accurate paleo-pressure distribution, the abnormal pressure characteristics are studied based on sonic logs and pressure testing data from 34 wells. The correlation between the abnormal pressure coefficient and its burial depth is obtained and applied to restore paleo-pressure distribution. The erosion thickness is calculated using depositional wave analysis technique, and the paelo-porosity is calculated based on the empirical equation between formation capillary pressure and porosity. The burial history is modeled using back-stripping technique.

The results suggest that: the common higher fluids potential area of the four formations is consistent with the center of source rock in the sag; E_s3, E_s2, and E_s1³ have three inherited flow convergence zones respectively. E_s1²⁺¹ have three relatively high fluid potential zones which alternate with two relatively low potential zones. These three inherited convergence zones and two lower potential zones are favorable for hydrocarbon accumulation; the sand bodies encircled by shale in the relatively high fluid potential zones are also possible perspective exploration areas in deep formation.

AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009