Influence of clayish minerals on the gas permeability of the Dagi-suite reservoirs at the Okhotsk oil-gas-bearing province (the shelf of Sakhalin)
The Okhotsk oil-gas-bearing province (offshore the Sakhalin Island) is a key player in gas supply of the Far East and the Asian-Pacific region. To develop resources of the continental shelf the significant capital and operational investment are necessary, that is why the offshore deposits are insufficiently studied, and the uncertainty of either their geological structure, or in-situ distribution of the parameters of productivity is rather high.Due to this fact, during the complex core tests the filtration properties, mineralogical and fractional composition of the Dagi reservoirs have been studied including a type and composition of the argillaceous cement. It is ascertained that the main agents of permeability and porosity of Dagi rocks are the clayish minerals, namely, content and composition of a clayish material. The correlations between the filtration properties of rocks and the composition and content of the clayish materials are derived. Presence of illites, smectites, and mixed lattice minerals seriously decreases gas permeability of rocks due to high values of specific surface area and cation exchange capacity of minerals.To estimate reservoir quality of rocks validly by means of well logging, it is recommended to take the mineralogical clayishness (according to X-ray diffraction analysis) as a criterion with regard to composition of argillaceous cement.