The methods of improving the technology of acid-proppant fracturing of carbonate reservoirs in the fields of Udmurtneft OJSC are considered that allow performing effective stimulation of wells taking into account the geological features of reservoirs that impede hydraulic fracturing. In Udmurtneft OJSC such geological features include large perforation intervals (up to 200 m from the bottom to the top of the perforation); the presence of undesirable nearby water - or gas-saturated layers; the properties of formations developed simultaneously are significantly different; lack of efficiency of reservoir pressure maintenance system; low reservoir pressures and low temperatures. In the article you can see the engineering solutions to address each factor that complicates performance of frac jobs. For highly partitioned formations with large perforation intervals, hydraulic fracturing is performed with placing sand in bottomhole during the injection process. This method of hydraulic fracturing is implemented according to the following scheme: at first stage the lower penetrated horizon is stimulated, then the proppant agent is put to the bottomhole to the specified interval of perforation, after setting of the sand (proppant agent) in the wellbore the reservoir is stimulated through the upper intervals. In the conditions of undesirable nearby water - or gas-saturated layers it is efficient to perform hydraulic fracturing with stage-by-stage acid injection alternating with shut-in followed by gradual increase of injection rate and subsequent fixing of the created fracture with the proppant agent. To stimulate the simultaneously developed layers with different properties hydraulic fracturing is carried out in accordance with the adaptive design, i.e. the design is changed during the injection process. At low reservoir pressure the optimal method is hydraulic fracturing with blocking composition of cross-linked gel injected at a high flow rate.
The application of the proposed methods to the technology of proppant-acid fracturing makes it possible to increase the efficiency of fracturing, to mitigate the risks during operations, to perform effective stimulation of wells in complex geological conditions, as well as to increase the number of candidate wells for fracturing and to expand the potential for drilling new wells in previously undeveloped areas.
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