Research On Influencing Factors And Evaluation Methods Of Water Activity In Water Drive Gas Reservoirs

Nowadays,the whole world is striving to promote efficient,clean and diversified energy transformation.China's energy structure is constantly improving.Natural gas resources will play an important role in the process of energy transformation.For the water-driven gas reservoir which has a good communication relationship with the water connection around,when the pressure wave propagates to the water body,the formation water begins to invade the gas reservoir.Water intrusion will seriously affect the development and production of gas reservoirs,reducing the production of gas wells as well as the recovery ratio.Severe water intrusion may lead to flooding of gas wells,even make the gas well out of production.Thus exerting an enormous effect on the development benefits of the entire gas reservoir.The 60-year natural gas industrialization process in Sichuan Province shows that water is generally produced during the development of gas reservoirs.Nearly 50%of the production wells rely on the drainage process to maintain production.In recent years,the implement of drainage and gas production technics of the old gas fields has been maintained at more than 300 times per year.The development of water-bearing gas reservoirs not only involves the application of geological and gas reservoir engineering,but also closely related to the drainage and gas production technics and the formation water reinjection project.The core of the development is whether it can correctly evaluate the energy and activity of water bodies in water-bearing gas reservoirs.Formulate corresponding measures to improve the development benefits of water and gas reservoirs.Based on the investigation of a large number of literatures,the main work of this paper is as follows:(1)Starting from the water invasion mechanism of water drive gas reservoir,the macro and micro mechanisms of water invasion and the main modes of water invasion are studied,and the relationship between water invasion mechanism,water invasion mode and water activity degree of gas reservoir is analyzed.It is clear that the two key factors affecting water activity degree of water drive gas reservoir are respectively:The energy of the water around the gas reservoir and the seepage passage between the gas reservoir and the water body are good or bad.It lays a foundation for subsequent model establishment and index calculation.(2)The seepage model of homogeneous edge water gas reservoir and heterogeneous edge water gas reservoir is established respectively,taking the seepage control area of single well with different heterogeneity as the main research object.Through programming calculation,the influencing factors and influencing degrees of water body activity in different heterogeneous percolation areas are clarified,and the knowledge of water invasion law and water invasion dynamics of water drive gas reservoirs is enriched.The following conclusions are drawn:the key influencing parameters of water body activity in quasi-homogeneous edge water gas reservoirs are reservoir permeability and water body multiple,in which permeability plays a decisive role and contains high permeability zones;The key influencing parameters of water body activity in heterogeneous edge water gas reservoir are the extremely poor permeability,the width of high permeability zone and the water body multiple of heterogeneous high permeability zone.Taking the ultimate recovery rate of gas well as the target,the influence of permeability range and water multiple on the key parameters affecting the target is analyzed,and the influencing factors chart of water activity degree of gas reservoir is formed,which can be used for the influence analysis of key parameters.Taking the gas well of S Carboniferous gas reservoir as an example,the correctness of the chart of influencing factors of water body activity in gas reservoir is verified.(3)In order to formulate reasonable development strategies for water-invaded gas reservoirs with different water body activity,the evaluation methods and evaluation indicators for evaluating water body activity in water drive gas reservoirs and gas well control areas are summarized.Taking single well as the research object,the water body activity degree in the control range of water-producing gas wells in S Carboniferous gas reservoir is evaluated,and the applicability of evaluation methods and indicators of water body activity degree is analyzed by example calculation.(4)In order to further increase the accuracy of judging water activity in gas reservoirs,the discriminant analysis method was introduced.Six evaluation indexes of water activity in production type were synthesized.Based on the production data of 101 gas wells,a quantitative evaluation model of water activity was established and a discriminant chart of water activity was formed.The chart was validated by the method of backdating estimation.There were only two misjudgements in 101 sample wells,and the accuracy of the model was 98%.Compared with the traditional method for evaluating water body activity in water drive gas reservoirs,this method is easier to obtain,simpler to calculate,and more accurate than single dynamic index.Therefore,it is more practical for real-time updating of production data in mines.Through the above work,a set of research methods for water body activity evaluation and water intrusion characteristics law of water flooding gas reservoirs is formed,which has certain guiding significance for the rational and efficient development of water flooding gas reservoirs.