Reservoir Characterization Of Argillaceous Dolomites And Dolomitic Mudstones Reservoir: Xiagou Formation Qingxi Sag In Jiu Xi Basin

The thick layers of argillaceous dolomites and dolomitic mudstones are the main source rocks and reservoirs in the Lower Cretaceous strata Xiagou Formation in Qing Xi Sag, Jiu Xi Basin has caused intensive interest but this unconventional reservoir as yet little known. This article using the data of drilling logging, core descriptions and mirco scopic slivers, by analyzing the rock formation, statistics the thickness of argillaceous dolomites and dolomitic mudstones percentages in G0~G1 layer of Xiagou formation to studies reservoir characterization.The rise and fall of lake level change and seasonal temperature changes affect the ancient lakes algae breeding- concentration- the demise of the life process. Along with the influence of seasonal temperature on lake water body vertical occur alternately, death of algae and carbonate lake basin surface water alternating bioclastic and deep water, forming rich organic matter of algae laminae.Since the argillaceous dolomites and dolomitic mudstones reservoir lies in facies of deep-lack, based on the former studies, determined the formation mechanism is the craterlike “white smoke” Jet – hydrothermal deposition and controlled by the alternation diadenetic effect to formed the thick muddy dolomite.Due to this genetic mechanism, dolomitic mudstones contains a lot of brittle minerals, such as feldspar, iron dolomite, present the characteristics of dual-laminar and tri-laminates, namely organic matter-rich strata of mud and brittle mineral composition of dolomite, feldspar and other thin laminae in the “layer cake” model of thin laminae of alternating layer structure.In the study area by the north east rift tectonic belt and north west of the control of the strike-slip structural belt, argillaceous dolomites and dolomitic mudstones reservoir distribution are often present north west extension, argillaceous dolomites and dolomitic mudstones reservoir distribution of sedimentary facies in west sag of semi deep lake- deep lake subfacies environment.In addition, the tectonic activities resulting in Jiu Xi Basin reservoir has lots of fractures which is good for hydrocarbon migration and accumulation. Fracture is an important reservoir argillaceous dolomites and dolomitic mudstones reservoir space, its development degree determines the capacity of oil and gas reservoir. Imaging logging data, according to the oblique fractures often have higher adsorption capacity and capacity, much to low Angle fracture(4°~45°) is given priority to, also have because of the high Angle of fracture formed by the tectonic compression(45o~80o) oblique fractures. Inter-layer horizontally to reservoir development also has certain ability and capacity. The microscopic observation results show that the micro crack width in 20~500μm range, the most can reach more than 1 mm wide. Better connectivity and micro cracks, communicate the rock pore and oil source rock.Reservoir characterization of argillaceous dolomites and dolomitic mudstones reservoir, conducive the understanding of the reservoir characteristics which can help to explore & develop the reservoir.