A brittleness evaluation method for shale gas reservoirs based on mineral content

Abstract

The invention discloses a mineral content-based brittleness evaluation method for a shale gas reservoir. By taking the brittleness of quartz as the standard, the relative brittleness degree, called as a mineral brittleness coefficient, of each essential mineral in the shale gas reservoir is determined; the essential minerals comprise the quartz, clay-contained quartz, kaolinite, Mexico clay, mixed clay, calcite, dolomite, rock salt, kerogen, perthite, anorthose, feldspar, anhydrite, zeolite and natrolite; the overall brittleness degree of reservoir rock is computed by utilizing mineral volume content and the brittleness coefficient of each mineral; the mineral volume content refers to the percentage that the volume of minerals in porous rock accounts for the total volume of the porous rock. The brittleness evaluation method is superior to a method, used in oil exploration industry at present, for evaluating brittleness by comparing the volume content of the quartz and carbonatite and the total volume of the minerals.

Description

technical field [0001] The invention relates to the field of rock physics and reservoir evaluation methods, in particular to a shale gas reservoir brittleness evaluation method based on mineral content. Background technique [0002] For shale gas reservoirs, since fracturing directly affects gas production, the prediction and evaluation of the brittleness of underground rocks determines the success of fracturing. Brittleness is an important mechanical property of materials. However, there is no consensus on the definition of brittleness, and different researchers propose different brittleness definitions or brittleness measurement methods according to different situations and measurement methods. However, based on a large number of test values, it can be considered that high brittleness values ​​represent: (1) low ductility, (2) easy cracking, (3) weak reservoir, (4) high compressive strength / Tensile strength, (5) high recovery force (elasticity), (6) high internal fricti...

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Problems solved by technology

This method has two defects. First, it does not consider the degree of brittleness of each mineral. For example, in formula (2), the coefficients of carbonate rock and quartz in the molecule are both 1, and quartz, calcite, and clay in the denominator are all 1. The coefficients are also 1, that is, the brittleness of quartz and carbonate rocks is considered to be the same. In fact, the brittleness of these two minerals is different, which will make the overall brittleness of the calculated rock wrong; second, Both of these methods do not take into account the minerals such as kerogen and feldspar in shale gas reservoirs, and shale gas reservoirs are characterized by complex minerals, containing a certain amount of kerogen, and feldspar is a common rock formation Minerals are bound to exist in rocks, and ignoring these minerals will also cause errors in the calculated brittleness value of the rock as a whole

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