Modeling of Gas Accumulation Dynamics in Foreland Thrust Belt, Kuqa Depression, Tarim Basin

Abstract

The foreland thrust belt is the main accumulation zone of oil and gas in the Kuqa Depression, with sufficient gas supply and strong filling. The differences of gas accumulation driving force in different zones divided by the Kelasu Fault have not been thoroughly studied. Through physical model experiments, we tested the gas breakthrough pressures with confining pressure ranges from 10 to 50 MPa, fitted the relationship between gas breakthrough pressure and confining pressure and then predicted the minimum driving force (critical filling pressure) needed for gas accumulation. Based on fluid inclusion data, formation pressure data and reconstruction of burial history, we recovered the paleo-pressure using numerical simulation. We built a pressure evolution model based on geologic condition and rebuilt the abnormal fluid pressure history of Jurassic hydrocarbon source rocks and Cretaceous Bashijiqike sandstone reservoir bed in different areas and geological histories. In order to quantify the contribution of source-reservoir pressure differential in gas accumulation, we introduced the concept of “impulse” in physics. The results showed that: (1) The reservoir fluid pressure of the Bashijiqike Formation experienced two stages: formation and development of abnormal fluid pressure caused by sedimentation and pre-buildup of abnormal fluid pressure caused by tectonic compression; (2) Source-reservoir pressure differential is different in different stages and different zones, showing strong in the early stage and weak in the late stage to the north of the Kelasu Fault and sustained differential to its south. From the early Kuqa age to the early Quaternary period (5.3Ma-1.6Ma), the pressure differential in the Kela zone of the northern area was greater than that in the Keshen zone of the southern area. Nowadays pressure differential is reversed in the northern area, but it still maintains sufficient filling power in the southern area; (3) Source-reservoir pressure differential is generally larger than critical filling pressure of gas, in accordance with gas filling dynamics condition; (4) The “impulse” trend of obvious increase in the southern area during the late accumulation period has a positive correlation with gas saturation. It provides a theoretical basis from the perspective of gas accumulation dynamics to predict new favorable zones.

AAPG Datapages/Search and Discovery Article #90217 © 2015 International Conference & Exhibition, Melbourne, Australia, September 13-16, 2015