Abstract
Purpose. Improving the producing capacity and ensuring the stable operation of gas wells that develop unstable, low-cemented reservoirs by preventing the sand entry from the reservoir by means of creating the cement stone with the corresponding values of strength and permeability in the bottomhole formation zone. Methods. The technological characteristics of the cementing slurry and the formed cement stone are measured using standard recording equipment. The cementing slurry consistency is measured with a pycnometer, the cement mixture spread ability – using AzNII cone, water separation is measured according to standard methods (DSTU BV.2.7 – 86-99), and the time of the cementing slurry hardening is determined on a consistometer KTS-3. The ultimate parameters of the stone strength during bending are determined on a special device for testing linear objects in tension, and compression – on a PSU-10 hydraulic press. Findings. The cementing slurry composition for creating the cement stone with the corresponding values of compression strength and gas permeability in the bottomhole formation zone has been developed, which includes oilwell cement, expanded perlite, non-ionic surfactant, plasticizer and water. Dependences of the cement stone compression strength and the stone permeability coefficient on the proportion of expanded perlite in the cementing slurry solution have been revealed. It is recommended to use the proposed cementing slurry for creating a cement stone with specified values of compression strength and permeability in the expanded well shaft in the interval of the producing reservoir. Originality. The optimal proportion of the expanded perlite in the solution has been found, at which the corresponding values of the compression strength (up to 4 MPa) and gas permeability (up to 3.47 μm2) of the cement stone is provided. Practical implications. When using the developed composition, it is possible to increase the yield of wells with unstable reservoirs and improve their working conditions by preventing the sand entry from the reservoir into the well.
Highlights
A significant amount of gas and gas condensate fields in Ukraine are at the final stage of development, which is characterized by a significant decrease in reservoir pressure, low yield of producing wells and the presence of factors complicating their work
Permeability in the range of 1.25-3.47 μm2 and compression strength of 4 MPa of the obtained cement stone make it possible to increase the yield of the well without sand entry after strengthening the bottomhole zone with an increased drawdown pressure on the reservoir, as well as to increase the overhaul period of the well operation
To prevent the sand entry from the reservoir into the well with an open hole, it is recommended to expand the well shaft in the interval of the producing reservoir according to known technology during the well construction for filling the formed hollow space with cementing slurry
Summary
A significant amount of gas and gas condensate fields in Ukraine are at the final stage of development, which is characterized by a significant decrease in reservoir pressure, low yield of producing wells and the presence of factors complicating their work. The complications typical for the final stage of field development include water flooding of wells and destruction of the bottomhole formation zone (BHFZ) in unstable (low-cemented) reservoirs. The operation of gas and gas condensate wells with unstable reservoirs is accompanied by the removal of rock particles from the reservoir and their accumulation at the well bottom with the sand plugs formation. It is confirmed in the research that the rock particles removal from the reservoir during the wells operation is accompanied by the formation along the fractures in the bottomhole formation zone of highly permeable channels with various widths and lengths, filtering gas and reservoir water [2]. The solid phase, when carried out of the producing reservoir, leads to instability and rock caving into the bottomhole zone, the formation of caverns, stuck oilwell tubing, collapse of the production string, abrasive wear of well equipment, and the formation of sand plugs in faces, which leads to additional resistance to gas movement and reducing the well yield [3]
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