Technique for automated calculation of technological parameters for non-Newtonian liquids injection into a well during workover is presented. At the first stage the algorithm processes initial flow or viscosity curve in order to determine rheological parameters and coefficients included in equations of rheological models of non-Newtonian fluids. At the second stage, based on data from the previous stage, the program calculates well design and pump operation modes, permissible values of liquid flow rate and viscosity, to prevent possible hydraulic fracturing. Based on the results of calculations and dependencies, a decision is made on the necessity of changing the technological parameters of non-Newtonian liquid injection and/or its composition (components content, chemical base) in order to prevent the violation of the technological operation, such as unintentional formation of fractures due to hydraulic fracturing. Fracturing can lead to catastrophic absorptions and, consequently, to increased consumption of technological liquids pumped into the well during workover. Furthermore, there is an increased risk of uncontrolled gas breakthrough through highly conductive channels.
Production well killing before workover operations in late-stage oil and gas-condensate fields can be complicated by abnormally low formation pressure, carbonate type of reservoir rocks, and high gas-oil ratio. These complications lead to the intensive absorption of technological fluids by the formation and gas ingresses, which, in its turn, increases the time of killing wells and putting them on production, reduction of productivity, and additional costs. Therefore, it is crucial to develop a high-performance well-killing composition that would allow improving the efficiency of killing wells in complicated geological, physical, and technological conditions at the expense of reliable overlapping of the perforation interval (or open wellbore) to prevent gas intakes and gas outflow from the formation. To develop blocking compounds, a set of laboratory tests has been carried out, including physical and chemical (determination of density, viscosity, thermal stability, sedimentation stability, etc.) and research of blocking and filtration properties of compositions during simulation of a fractured reservoir. In the course of laboratory tests, the choice of fractional composition and polymer filler concentration was substantiated in the blocking emulsion and polymer compositions to increase the efficiency of their application under the complicated conditions of killing oil wells. As a result of laboratory research and field tests, the emulsion and polymer blocking compositions containing bridging agent (microcalcite) were developed, which increase the oil well killing efficiency by preventing the absorption of technological fluids in the formations and, as a result, preserving its productivity.
The investigations of thermostability and rheological properties of the hydrophobic emulsion compositions; modeling the process of filtration in interstratificated and heterogenetic layers, and filtration in conditions maximally approximated to formation conditions were provided. The optimal composition of process liquids which is able to regulate filtration properties of reservoir-formation of the bottom hole formation zone is developed.
Based on the investigations of stability and rheological properties of the hydrophobic emulsion compositions, and on modeling the process of filtration in conditions maximally approximated to formation conditions, the optimal composition of process liquids which is able to regulate filtration properties of reservoir-formation of the bottom hole formation zone was developed.
The method of calculation pumped volumes of flow angularity compositions in injection wells, which based on combination of the seepage theory, laboratory investigation and field experience is developed.
The experience of oil field development shows that filtration parameters of bottomhole formation zone are gradually decreasing as a result of killing and operation of wells. The main reason for this is the use of water-based process fluids, which are now widely used in the oil industry. Currently, considerable attention is being paid to increasing reservoir penetration area by using active acids to stimulate oil and gas wells. Hydrocarbon-based compositions, in particular invert emulsions, are alternative systems for solving these problems.
The problem of maintaining tightness of tubing annulus in gas and gas condensate reservoirs is especially urgent. Leakiness is caused by the fact that formation fluid in such reservoirs often contains aggressive components - hydrogen sulfide, carbon dioxide, as well as poor insulation of formations containing these agents. This leads to various complications during well operation.