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EFFECT OF METAL FIBERS ON THE PROPERTY OF WELL CEMENT

Nowadays more oil and gas fields are developed in unconsolidated sandstone. When the formation consists of poorly cemented rocks, the connections between the rock particles are broken under the influence of forces acting in the bottomhole during oil production (wells), and the rock skeleton is intensively disintegrated and brought to the well by fluid flow. The sand production is considered undesirable product and the control of sand production is considered as one of the main concerns of production engineers. It can damage downhole, and surface production facilities, also increasing the risk of catastrophic failure. Choosing a method for preventing formation sand production depends on different reservoir parameters. The analysis of the production wells, where measures are taken to prevent the sand production, showed that the most effective method is to cover the bottom hole with various mortar materials. However, the current methods of bottomhole strengthening with cement mortars have a number of technological shortcomings which can include limited ductility and little resistance to cracking. According to the results, the efficiency of bottomhole reinforcement in the Absheron field is 40-50%. The reason for the low efficiency of this method is mainly the presence of lithostatic pressure and dynamic (perforation, sliding and lifting) loads applied to the cement barrier in the wellbore area. It is known that the weakest part of cement stone, prone to collapse and wear, is the perforation holes. During the oil production, the volume of sand increases that brought to the well, and around the perforation holes that on the cement stones are formed the collapses and fractures. Due to its low deformation and crack resistance, it cannot withstand these impact loads. Hence there is a need to reinforce the property of cement.
The article presents the results of experimental studies of fiber-reinforced cement recommended for improving the quality of bottomhole coverage in increasing dynamic impact intervals. One of the promising directions to increase the resistance of the cement barrier under dynamic loads is its strengthening against compression and bending, using the principle of composition, which provides the compression resistance of the cement matrix. The most important properties of cement stone can be effectively regulated by using metal fibers, which allow implementation of the principle of composition in cement barrier. The main physical and mechanical properties of the cement burrier formed as a result of increasing the fiber concentration in the tampon solution change. Reinforcing metal fibers, uniformly distributed in the matrix and having different directions, received forces in any direction, preventing the formation and development of cracks in the cement stone. The metal fibers are randomly oriented and uniformly distributed throughout the volume, work together with the matrix due to the adhesion forces, and form a compact shape. When fiber adhesion is disrupted, the fibers prevent the growth and development of cracks by maintaining the integrity of the cement stone. Based on this principle, a new dispersion-enhanced buffering material consisting of a mixture of quartz sand and metal fibers was developed. Experiments were carried out to improve the physical and mechanical properties of the cement system (strength, fluidity, setting time, etc.) in the laboratory. Studies have taken a certain proportion of the water-cement mixture. Metal fibers of different quantities and lengths were added during the experiments to determine the mechanical properties of the cement stone. The test period, day and the curing temperature performed at different intervals according to the mixtures. The article shows the positive effect of fiber on the main properties of buffering solutions and the resulting stone, both theoretically and experimentally. The choice of the optimal method of cement stone reinforcement is the result of laboratory experiments. Following the results obtained, recommendations were given for the optimization of cement compositions.
Keywords: cement stone, cement barrier, well area, dynamic loads, fiber, reinforcement, destruction, deformation, expansion.