Analysis of the formation conditions of Mesozoic secondary oil and gas reservoirs in Halahatang-Hade area of the Tabei Uplift

Abstract

Objective The Mesozoic strata in the Halahatang-Hade area of the Tabei Uplift belt, Tarim Basin, cover an area of more than 30 000 km2. It has a large monoclinic background, with active hydrocarbon displays and great exploration potential, but no exploration breakthrough have been made for many years. The discovery of the adjacent SINOPEC mining area promoted exploration in the area. Methods Based on the newly obtained 3D seismic data and a regional geological overview, the oil source conditions, structural and evolutionary characteristics of strike-slip faults, and formation and sealing conditions of lithologic traps were systematically analysed, and the reservoir formation pattern and favourable exploration directions in this area were clarified. Results In this area, fluvial-delta sedimentary systems developed in the Mesozoic, including a NE-SW-trended delta sand-body developed during the Triassic, the SE-NW-directed shallow water delta sand-bodies developed during the Early Jurassic and Cretaceous, and a large scale of continuous braided river sand-body developed during Late Cretaceous. The study area had experienced three uplift episodes and five faulting episodes. The Triassic-Jurassic fault system accompanied by the Palaeozoic fault system show NE-SW-striked in echelon. The front edge of the Cretaceous and Jurassic shallow water deltas was spliced with a single body or multiple bodies covered with mudstone to form lateral occlusion, which combined with an upwards-dipping fault to form a lithology-fault trap. The Triassic striped sand-body spread in the southeast direction and formed lithology, and the mudstone shading outside the channel at the bend of the large river channel formed a lithological trap. Hydrocarbon sourced from Palaeozoic palaeo-accumulations, migrated through Palaeozoic-Ordovician faults, and directly or successively charged into the Mesozoic trap through the Mesozoic fault. Conclusion Based on the hydrocarbon accumulation model, it is believed that the potential exploration areas in the study area mainly include the Jurassic-Cretaceous Shushan River formation Delta front lithological reservoir of the northern strike-slip zone, the delta front sand-body on the north side of the Triassic, and the southern channel sand-body lithological trap, and the northern Triassic descending area covered with small fan lithological traps. The three controlling factors, fault assemblage, sand-body distribution, and mantled mudstone shielding, and their effective allocation are important for guaranteeing the formation of favourable lithologic and lithologic fault combination traps in the large slope areas of the Tabei Uplift belt. The research results point out the direction of further hydrocarbon exploration in this area and are important for guiding hydrocarbon reservoir exploration of lithologic and lithologic fault combination traps in other areas.

Keywords

• secondary oil and gas reservoir
• lithologic trap
• mesozoic
• halahatang-hade area
• tabei uplift