Horizontal well is an important way to develop thin reservoir with edge-bottom water aquifer. For the horizontal well near oil–water contact, the reservoir have the features of edge water and bottom water at the same time. The productivity formula of horizontal well in pure edge water or pure bottom water reservoir is not fully applicable to this type of reservoir. For the heterogeneous reservoir with composite water aquifer, the horizontal well is divided into multiple well sections by using the concept of multi-segment well. Based on the seepage mechanics theory and potential superposition principle, considering the mutual interference between multi well sections, the productivity formula of horizontal well in heterogeneous reservoir with composite water aquifer is established. The new productivity formula considers the effect of reservoir heterogeneity, the quasi-linear flow of lateral edge water and the ellipsoidal flow of vertical bottom water. It can effectively determine the influence range and drainage distance of edge water in a heterogeneous reservoir with composite water aquifer. According to the test data of horizontal wells in Weizhou 11-1 oilfield, the drainage distancebof edge water is fitted and used to predict the productivity of new wells, and the result is very good. The research result lays a foundation for productivity prediction of horizontal well in heterogeneous reservoir with composite water aquifer.

Production decline analysis is a simple and efficient method to forecast production dynamics of shale gas. The traditional Arps decline model is also widely used in the production decline analysis of shale gas, but an obvious error is often generated. Based on the Weibull and χ² probability density distribution function, the monotonic decreasing production prediction equations of shale gas are established. It is deduced that recently, the widely used Duong model is essentially a Weibull probability density distribution model. Decline analysis results of production data from actual shale gas well and numerical simulations indicate that the fitting results of the Weibull (Duong) model and χ² distribution model are better than the Arps model whose deviation of early data is large. For a shale gas reservoir with very low permeability, pressure conformance area is small and it is obviously influenced by fractures. Early shale gas production rate mainly contributed to by fractures declines quickly and the later production rate mainly contributed to by the matrix declines slowly over time. The production decline curve has obvious long-tail distribution characteristics and it is a better fit to the data with a χ² distribution model. As for the increase of permeability, the fitting accuracy of the Weibull (Duong) model gradually becomes better than the χ² distribution model. Research results provide theoretical guidance for choosing a reasonable production decline model of a shale gas reservoir with a different permeability.

Complex fracture systems including natural fractures and hydraulic fractures exist in shale gas reservoir with fractured horizontal well development. The flow of shale gas is a multi-scale flow process from microscopic nanometer pores to macroscopic large fractures. Due to the complexity of seepage mechanism and fracture parameters, it is difficult to realize fine numerical simulation for fractured horizontal wells in shale gas reservoirs. Mechanisms of adsorption–desorption on the surface of shale pores, slippage and Knudsen diffusion in the nanometer pores, Darcy and non-Darcy seepage in the matrix block and fractures are considered comprehensively in this paper. Through fine description of the complex fracture systems after horizontal well fracturing in shale gas reservoir, the problems of conventional corner point grids which are inflexible, directional, difficult to geometrically discretize arbitrarily oriented fractures are overcome. Discrete fracture network model based on unstructured perpendicular bisection grids is built in the numerical simulation. The results indicate that the discrete fracture network model can accurately describe fracture parameters including length, azimuth and density, and that the influences of fracture parameters on development effect of fractured horizontal well can be finely simulated. Cumulative production rate of shale gas is positively related to fracture half-length, fracture segments and fracture conductivity. When total fracture length is constant, fracturing effect is better if single fracture half-length or penetration ratio is relatively large and fracturing segments are moderate. Research results provide theoretical support for optimal design of fractured horizontal well in shale gas reservoir.

The old well sidetracking technology is an effective means to stabilize production and increase recovery in later stage of gas field development. Based on economical and reservoir geologic parameters of Sulige low-permeability gas field in China, method and procedure of old well sidetracking selection standards are established, which can effectively improve the sidetracking effect and adequately develop remaining gas. Comprehensively considering corresponding economic parameters including sidetracking drilling cost, operating cost, management cost, gas production rate and gas price, recoverable reserve standard of sidetracking well is determined first. According to gas recovery, gas-bearing area, porosity and gas saturation, standards of remaining geological reserve, reserve abundance and gas pay thickness of sidetracking well are obtained. According to extension direction and distribution characteristics of the sand body in research area, numerical simulation conceptual model of typical sidetracking horizontal well is established, and then standards of old gas well production rate and gas cumulative production rate for sidetracking are obtained. According to the standards, well Su 36-6-9CH is selected to be sidetracked as a horizontal well and its development effect is good. The method has important value of popularization and application in similar low-permeability gas reservoir.

Condensate oil and water invasion coexist in the condensate gas reservoir with bottom water. Because of influences of condensate oil pollution and water invasion, gas recovery obviously decreases. There are many factors influencing water invasion in a condensate gas reservoir with bottom water, including static petrophysical properties and dynamic operational conditions. Various factors play different roles in the process of water invasion, and the comprehensive effects of them on water invasion are difficult to be determined because these factors interfere with each other. With gas reservoir engineering method and numerical simulation technology, the factors including acuifer size, height of water avoidance, permeability, effective gas pay thickness, condensate oil saturation and gas well production rate on water invasion are researched. Water breakthrough time, stable production period and gas recovery are calculated for different cases under different parameter combinations through fuzzy comprehensive evaluation and orthogonal experiment design. Then sensitivities of these factors are analyzed and main factors influencing water invasion are selected and sequenced. The research supply theoretical basis for preventing and controlling water invasion thus improves development effect of condensate gas reservoir with bottom water.