Gas Well Workover Low Damage Temporary Plugging Gel System Research

Gas well design idea of temporary plugging fluid system for "plugging have to live, have to untie".At home and abroad have developed a number of plugging agents with different characteristics,such as pre-crosslinked polymers temporary plugging agent, adaptive broad spectrum temporary plugging agents have good sealing effect. This paper is based on the development of basic recipe temporary blocking agents as a basis, depending on the circumstances of different wells as well temperature, depth, casing, formation pressure, formation fluids and other differences, specific technical requirements of targeted, selected as the type of temporary blocking agent, gelling properties, broken plastic methods, gel breaking time control,forming a temporary plugging system through the different components of the preferred fluid system,and the temporary plugging fluid system to conduct a comprehensive evaluation.This paper mainly describes research on the development of a low pressure gas well suited Changqing area workover temporary plugging gel isolation system,suitable for conventional low pressure gas well workover temporary plugging, wells with pressure workover annulus temporary plugging operations.The first step of the Changqing Oilfield related block gas reservoir physical characteristics and properties of the formation fluid, respectively Wushenqi block and Jingbian block. Collecting 14 Wells data from Wushenqi block, statistics of 14 Wells production interval porosity, permeability and formation water salinity, each well production zone of formation pressure, the content of hydrogen sulfide in the gas production.Collecting 23 Wells data from Jingbian block, statistics of 23 Wells production interval porosity, permeability and formation water salinity, each well production zone of formation pressure, the content of hydrogen sulfide in the gas production.The second step, about the workover temporary plugging fluid system development and for the screening of the gel system of optimization of strengthening agent.The first is to select thickener:guanidine gum thickener, a cellulose derivative thickening agent, polyacrylamide thickener.Through experiments on guar gel system, CMC gel system and HPAM gel system to compare the three gel system screening, the final selection of HPAM gel system.The second is to determine the gel system strengthening agent optimization:Gel system under the effect of crosslinking agent, viscosity increased significantly, but during the gas well workover operations, requires a certain depth of gel stopper has a certain strength, can hang a wall, can effectively separate the upper pressure well liquid, good gas shut-off. On the basis of consulting a large number of literature to choose two materials: glass fibre and starch. After experimental verification choose modified starch as strengthening agent of gel system.In addition there are a thickener, an oxygen scavenger, clay stabilizers are preferred.The third step, the performance evaluation of workover of temporary plugging fluid system, such as temperature resistance, bearing capacity, gel breaking flowback and core damage experiment.Gel System Requirements temperature resistance temperature resistance at 120℃; bearing capacity required to meet the same performance under pressure differential 3-5MPa; Gel breaking flowback demands to break the viscosity of the gel after 30 mpa.s;reservoir sensitivity damage experiments are divided into liquid and gel breaking liquid on the reservoir permeability damage evaluation.The results show that despite under the condition of high temperature gel system is difficult to do 1-3 days break time controllable, which need further research, the rest can satisfy the requirements of project content.Through experiments the following conclusions:(1) By regulating crosslinking system, and can satisfy the gelling time within 2-5 hours manageable, with the pump truck pump injection, the viscosity is not higher than 100mpa.s.(2) Gel temperature resistance of temporary plugging agent system reaches more than 120℃..(3)100m of temporary plugging gel in 5-1/2 casing, can withstand pressure difference to 3-5 MPa, temporary plugging agent does not occur to take off the wall.(4) By adjusting the breaker system, the low temperatures (40℃-60℃) can satisfy the gel breaking time controlled within the range 1-3 days; Gel system hydration performance good flowback after break, viscosity is not higher than 30 mpa.s.(5)After the completion of gel breaking of reservoir permeability damage is less than 20%, static simulation core permeability recovery value reached more than 80%.