Changing reservoir parameters during exploitation of fields/underground gas storages (through the example of Garadag area, Azerbaijan)

The paper presents the findings of studying deformational changes in rocks connected with development of oil and gas fields and operation of underground gas storages (UGS) through the example of Garadag field/UGS in the South Caspian Basin (SCB). On the basis of repeated well-logging measurements, it was found that over relatively short monitoring period (from 8 months to 2.5 years), development of VII level of the productive stratum (Lower Pliocene) of Garadag gas condensate field in the South Caspian Basin led to decreasing permeability of rocks in the range from 1.2 to 4.9 mD, with pressure drop from 2.4 to 11.7 MPa. The relative decrease in permeability ranges from 41 to 56%, while the higher values are typical for highly porous rocks. It is shown that multiple cycles of changing loads on the stratum in the process of the field/UGS development also contribute to the development of deformational changes in the rock, which lead to disruption of the rock matrix. This conclusion is supported by precipitation of about 25 - 30 tons of sand in the separator and liquid tank at the Garadag UGS facility in the end of each season. The sand is a product of rupturing rocks of the underground reservoir. This leads to irreversible changes in permeability and porosity of the reservoir rocks, which are sharper reflected in the change in the rock permeability. Deformational changes in the stratum caused by exploitation of the field and UGS lead to decreasing well productivity and injectivity.

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