Destruction of hydrocarbon reservoirs due to tectonic modifications: Conceptual models and quantitative evaluation on the Tarim Basin, China

摘要

The Tarim Basin in China is a complicated superimposed basin with four periods of hydrocarbon accumulations and three periods of modifications due to tectonic movements, forming complicated hydrocarbon reservoirs, many of which have gone through reservoir migration, reservoir scale reformation, reservoir damage and phase alterations a result of the tectonic events. Due to the complexity, the hydrocarbon exploration in this region has low success drilling rate. It is of great importance to study the destruction to the early hydrocarbon accumulations by the tectonic movements and quantitatively evaluate the remaining resource for understanding the current hydrocarbon distribution and guiding the exploration. This study analyzed six periods of large tectonic events in the Tarim Basin, and found the destroyed hydrocarbon volume was mainly controlled by four geological factors, including the ratio of the destroyed to the original hydrocarbon amount, tectonic event number and sequence, and the cap seal capacity. Larger ratio of destroyed hydrocarbon, less tectonic event number, later sequence and stronger cap seal capacity lead to more hydrocarbons preserved through the tectonic events. Based on the geological analysis, we established quantitative relationships among the destroyed hydrocarbon volume by the tectonic events (Q(1)), the volume of primary hydrocarbon accumulation (Q(0)), the ratio of destroyed hydrocarbon (K-1), the tectonic event number (n) and sequence (i), and cap seal capacity (fc). Using these relationships and the calibrated geological parameters, we delineated the hydrocarbon accumulation and destruction history and quantified the hydrocarbon loss due to the tectonic events for both the Tazhong area and the whole Tarim Basin. In the Tazhong area, four major accumulation events occurred at 510 Ma, 298 Ma, 227 Ma and 38 Ma with each accumulation underwent 68%, 59%, 28% and 0% of hydrocarbon loss due to later tectonic events. In total, over 60% of the original hydrocarbon reserves have been destroyed in the Tarim Basin, with an estimate of ca. 1.9 billion tons remaining hydrocarbons in the Tazhong area. At present, more than 95% oil and gas reservoirs and over 93% high quality exploration wells are located in the areas with high remaining resource potential predicted in this study, whereas 70% non-commercial production wells are located outside. Overall, this work shows that a careful evaluation of the damage to reservoirs from tectonic events can considerably enhance the success rate of hydrocarbon exploration.