Abstract
The exploration of shale gas in Fuling area achieved great success, but the reservoir characteristics and gas content of the lower Jurassic lacustrine in the northern Fuling areas remain unknown. We conducted organic geochemical analyses, Field Emission Scanning Electron Microscope (FE-SEM), X-ray diffraction (XRD) analysis, high-pressure mercury intrusion (MIP) and CH4adsorption experimental methods, as well as NMR logging, to study mineral composition, geochemical, pore structure characteristics of organic-rich shales and their effects on the methane adsorption capacity. The Da’anzhai shale member is generally a set of relatively thick (avg. 75 m) and high carbonate-content (avg. 56.89%) lacustrine sediments with moderate total organic carbon (TOC) (avg. 1.12%) and thermal maturation (Vitrinite reflectance (VR): avg. 1.19%). Five types of lithofacies can be classified: marl (ML), calcareous shale (CS), argillaceous shale (AS), muddy siltstone (MS), and silty shale (SS). CS has good reservoir quality with a high porosity (avg. 4.72%). The small pores with the transverse relaxation time of 0.6–1 ms and 1–3 ms comprised the major part of the porosity in the most lithofacies from Nuclear magnetic resonance (NMR) data, while the large pore (>300 ms) accounts for a small porosity proportion in the CS. The pores mainly constitute of mesopores (avg. 23.2 nm). The clay minerals with a large number of interparticle pores in the SEM contributes most to surface area in the shale lithofacies with a moderate TOC. The adsorption potential of shale samples is huge with an average adsorption capacity of 4.38 mL/g and also has high gas content (avg. 1.04 m3/t). The adsorption capacity of shale samples increases when TOC increases and temperature decreases. Considered reservoir properties and gas properties, CS with the laminated structures in the medium-upper section of the Da’anzhai member is the most advantage lithofacies for shale gas exploitation.
Highlights
A great success of shale gas exploration has been made in a Fuling gas field
Recent studies focuscapacity on the pore geochemical gascharacteristics content is notofonly a key factor of favorable shale gas areaThere evaluation, and concerning controls whether the Da’anzhai member lacustrine shale is little research the shale reservoir has a commercial exploration value or not influence of lacustrine shale reservoir characteristics on the adsorption capacity and total gas
The organic matter (OM) type in vertical transitioned from mainly typeII2 bitumen“A” content of 20 samples vary between 0.01% and 0.19% with an average value of 0.11%
Summary
A great success of shale gas exploration has been made in a Fuling gas field. Recently, many more oil and gas discoveries in lacustrine shale of the Lower Jurassic succession (e.g., Da’anzhai member shale) in the northern Fuling area gives a rise to the possibility of nonmarine shale gas accumulation in neighboring areas [1,2]. Recent studies focuscapacity on the pore geochemical gascharacteristics content is notofonly a key factor of favorable shale gas areaThere evaluation, and concerning controls whether the Da’anzhai member lacustrine shale [3,4,5]. Influence of lacustrine shale reservoir characteristics on the adsorption capacity and total gas In this study, we gas present a comprehensive approach mineralshale composition and geochemical content. 4adsorption experiments, as well as NMR well logging, to (1) determine the mineral composition members; (2) study the influence of continental reservoir characteristics on shale gas properties; and geochemical, pore structure and petrophysical of the different shale the lithofacies (3) optimize the advantageous shale lithofacies tocharacteristics provide guidance for selecting target in shale the Da’anzhai members; (2) study the influence of continental reservoir characteristics on shale gas gas layers.
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