Integral and differential approaches to determining the volumetric compression of rocks caused by changes in the stress state are considered. Changes in the volume of the pore space of rocks are analyzed with an increase in its all-round compression. Estimation of changes in the compressibility coefficients of reservoirs due to the development of fields is an urgent problem, since the spread in the values of compressibility factors reduces the adequacy of estimates of changes in the physical properties and subsidence of the earth's surface of developed fields and underground gas storages. This parameter is key in assessing the geodynamic consequences of the long-term development of hydrocarbon deposits and the operation of underground gas storage facilities. Approaches to the assessment differ in the use of cumulative (integral) or local (differential) changes in porosity with a change in effective pressure. It is shown that the coefficient of volumetric compressibility of pores calculated by the integral approach significantly exceeds its value calculated by the differential approach, which is due to the accumulative nature of pore compression with an increase in effective pressure. It is shown that the differential approach more accurately determines the value of the pore compressibility coefficient, since it takes into account in more detail the features of the change in effective pressure.
The paper is devoted to studies of the volumetric response of rocks caused by changes in their stress state. Changes in the volume of fracture and intergranular components of the pore space based on measurements of the volume of pore fluid extruded from a rock sample with an increase in its all-round compression have been experimentally obtained and analyzed. Determination of the fracture and intergranular porosity components is based on the authors' earlier proposed method of their calculation using the values of longitudinal wave velocity and total porosity. The results of experimental and analytical studies of changes in porosity and its two components (intergranular and fractured) under the action of effective stresses are considered. This approach allowed the authors to estimate the magnitude of the range of changes in the volumetric compressibility of both intergranular pores and fractures in a representative collection of 37 samples of the Vendian-age sand reservoir of the Chayanda field. The method of separate estimation of the compressibility coefficients of fractures and intergranular pores is proposed, their values and dependence on the effective pressure are experimentally obtained. It is determined that the knowledge of the values of fracture and intergranular porosity volumetric compressibility will increase the reliability of estimates of changes in petrophysical parameters of oil and gas reservoirs caused by changes in the stress state during the development of hydrocarbon fields.
It was shown on example of a number of deposits that space contemporaneity of emergency situations at wells and pipeline systems to fault zones finds its natural explanation within the concepts of existence of SD processes in such zones. In such situation it is essential to conduct very thoughtful system of diagnostics of crust fields with fluctuation deformation characteristics. For that purpose follow-up realization of three interconnected procedures must be conducted: detailed and measurement-assured monitoring (geodynamic test-area), complex several-variant interpretation of results of the monitoring and selection of different scenarios of possible negative contour, determination of the level of geodynamic risk, forecasting the environmental, social and economic consequences, and formulating strategies for preventive arrangements.
Within the framework of the engineering design of the join up of additional wells of Lower Cretaceous sediments at the Yamburg oil-gas condensate field the evaluation of geodynamic consequences of long-term exploitation of the mentioned field was performed, as well as the hazardous geodynamic process permanent survey program was developed.
Results of repeated leveling observations on the geodynamic range, organised on the Muhanovsky oil field (Samara region) are presented. It is shown that the most abnormal vertical displacement of a terrestrial surface (120 mm) are dated to fault to a zone located in the western part of the field and represent an essential danger to objects of the infrastructure of an oil field. Vertical displacement along the profile crossing Otradny town, located at oil field, are insignificant and it makes value of 2 to3 mm.
