Controls of Acid‐sensitive Minerals on Reservoir Sensitivity Testing: An Example from the Silurian Kepingtage Formation in Tazhong Area, Tarim Basin

Abstract

The Silurian Kepingtage Formation in Tazhong area is regarded as an acid‐sensitive hydrocarbon reservoir. However, formation mechanism of acid‐sensitive of the reservoir cannot be interpreted by the existing acid‐sensitive evaluation criterion based on damage rate. The contents of acid ‐sensitive minerals illustrated by bulk‐rock XRD, scanning electron microscopy and clay mineral composition analysis exert the dominant control on acid‐sensitive flow testing of the reservoir. The iron‐ bearing minerals (including pyrite cements and chlorite cements) mainly deteriorate reservoir quality, while the iron‐free minerals (including calcite cements and dolomite cements) mainly improve permeability. The permeability variation of the tested samples is controlled by the relative content of two acid‐sensitive minerals. On the basis of newly established sensitivity mechanism and its influence on permeability, the corresponding ion (Fe2+) stabilizer was added to the acidizing fluids during the acidification reconstruction, which inhibited the negative factors of acid‐sensitive minerals and improved the target layer quality effectively.

The chemical damage of sandstone after sulfuric acid-rock reactions with different duration times and its influence on the impact mechanical behaviour

“…In terms of AEP, Liao et al [ 31 ] explored the feasibility of permeability improvement of acid-rock reaction by the indoor plunger experiment and found that the acidic fluid systems (including hydrochloride acid, formic acid and acetic acid) can significantly improve the core permeability with an average percentage increase of 763 %. Han et al [ 37 ] investigated the influence of iron-bearing minerals and iron-free minerals on the reservoir permeability and provides theoretical guidance for the application of AEP. Sun et al [ 38 ] further studied the internal mechanism of acid-rock reaction on the reservoir permeability, the enlarged small and large pores/throats induced by the chemical corrosion contributed to the permeability enhancement of reservoirs.…”