Performance Of Fractured Horizontal Wells Research Articles

Production simulation and prediction of fractured horizontal well with complex fracture network in shale gas reservoir based on unstructured grid

In order to accurately simulate the productivity variation characteristics of fractured wells with complex fracture network in shale gas reservoir, based on the multiple migration mechanism of shale gas, the micro-seismic data and discrete fracture model were used to characterize the fracture geometry and complex boundary characteristics, and the comprehensive seepage mathematical model of fractured wells with complex fracture network was established based on the dual porosity-discrete fracture model, and the numerical solution was carried out by combining the unstructured grid and the control volume finite element method. The sensitivity analysis of the influence of key parameters such as fracture conductivity, physical property difference in composite area and Langmuir volume on the production performance of fractured horizontal wells is carried out. This study provides theoretical methods and calculation tools for accurate prediction of productivity change and optimization of production system of fractured horizontal wells with complex fracture network in shale gas reservoirs.

Pressure-Transient Performances of Fractured Horizontal Wells in the Compartmentalized Heterogeneous Unconventional Reservoirs

In order to investigate pressure performance of multiple fractured horizontal wells (MFHWs) penetrating heterogeneous unconventional reservoir and avoid the high computational cost of numerical simulation, a semi-analytical model for MFHWs combining Green function solution and boundary element method has been obtained, where the reservoir is divided into different homogeneous substructures and coupled at interface boundaries by plane source function in a closed rectangular parallelepiped. Hydraulic fractures are assumed uniform flux and dual porosity model is used for natural fractures system. Then the model is validated by compared with analytical solution of MFHWs in a homogeneous reservoir and trilinear flow model, which shows that this model can achieve high accuracy even with a small interface discretization number, and it can consider the radial flow around each hydraulic fractures. Finally, the pressure responses with heterogeneous parameters of reservoirs are discussed including heterogeneous permeability, non-uniform block-length and fracture half-length distribution as well as dual porosity parameters like elastic storage ratio and crossflow ratio.

A dynamic prediction model of pressure-control production performance of shale gas fractured horizontal wells and its application

For clarifying the inherent relation between relieving fracture closure and improving the EUR by adopting the pressure-control production system for shale gas fractured horizontal wells, and the significance of pressure-control production for gas reservoir engineering, a dynamic formation–fracture coupling prediction model for production performance of fractured horizontal wells was established and solved, with the finite conductivity fracture as basic flow unit and the variable stress sensitivity coefficient introduced. Through a comparison of the calculated results from the established model, classical model and numerical modeling by the Saphir software, the effect of characteristic parameters of stress sensitivity and pressure-control production system on the production performance of fractured horizontal wells was analyzed and verified in two wells. The results show that (1) the calculated results from the established model are basically consistent with those from the classical model and the numerical modeling by the Saphir software; (2) the existence of stress sensitivity makes the fracture conductivity decline with the production of gas wells, which leads to the decrease of cumulative gas production; the greater the stress sensitivity, the greater the decrease of cumulative gas production; (3) although the initial gas production and cumulative gas production of shale gas gained by the pressure-control production system are low compared with those by the pressure-release production system, the ultimate cumulative gas production is higher. Thus, it is more reasonable to adopt a long-term pressure-control production system for shale gas fractured horizontal wells. In conclusion, the research results provide a theoretical support for the popularization of pressure-control production system of shale gas wells.

A semi-analytical model for investigating the productivity of fractured horizontal wells in tight oil reservoirs with micro-fractures

Combining horizontal drilling with hydraulic fracturing has become a well-established technique to improve well productivity in tight oil reservoirs. The existence of micro-fractures in these reservoirs affects the fluid flow process as well as the productivity. However, current models for evaluating the well performance of fractured horizontal wells containing micro-fractures lack accuracy. Hence, the objective of this study is to build an efficient model to analyze well productivity, considering the effects of micro-fractures. A novel flow model for multi-fractured horizontal wells was established, considering the effect of micro-fractures on the fluid flow. Subsequently, we built a reservoir model based on the typical fracture and fluid properties of a tight oil block in the Daqing oil field, China. Good agreement between the prediction results and field data was obtained, indicating that the effect of micro-fractures on well productivity cannot be neglected. Further study reveals that micro-fractures essentially function as a joint connecting reservoir matrix and have a persistent impact on well productivity. Micro-fractures can promote well productivity; however, if the value of micro-fracture permeability increases, this promotional effect will slow down. Well productivity can be considerably improved as an increase in micro-fracture percentage. Finally, a series of sensitivity studies were conducted to identify the effects of critical parameters on well productivity. Results show that reservoir permeability significantly influences well productivity, followed by reservoir effective thickness, micro-fracture percentage, fracture number, hydraulic fracture half-length. Pressure sensitivity coefficient, threshold pressure gradient and micro-fracture permeability have the least effect on well productivity. This work provides a sophisticated and efficient tool to evaluate the productivity of multi-fractured horizontal wells in tight oil reservoirs with micro-fractures.

Well Testing Model of Multiple Fractured Horizontal Well with Consideration of Stress-Sensitivity and Variable Conductivity in Tight Gas Reservoirs

Multiple fractured horizontal wells have been widely used to develop unconventional tight gas reservoirs. Currently, many well testing models were established to study the performance of fractured horizontal wells in tight gas reservoirs. However, none of these models thoroughly takes stress-sensitivity of natural fractures and variable conductivity of artificial fractures into consideration. Based on the consideration of stress-sensitivity of natural fractures and variable conductivity of artificial fractures, a novel well testing model for fractured horizontal well in tight gas reservoirs is proposed. And the semianalytical solution of this new model is obtained by dividing the artificial fracture into different segments under the integrative methods of Laplace transformation, point source function, perturbation theory, superposition principle, and Stehfest numerical inversion. After validation, the semianalytical solution is consistent with that of Zerzar’s model (2004). Also, typical pressure and pressure derivative curves are plotted. According to typical curves, seven regimes can be derived, namely, bilinear flow, linear flow, early-time pseudoradial flow, biradial flow, intermediate-time pseudoradial flow, and pseudo-steady state interporosity flow, and late-time pseudoradial flow can be identified. In addition, this paper analyzes the impact on pressure and pressure derivative curves exerted by variable conductivity and stress-sensibility. The results show that variable conductivity mainly affects the early flow regimes, including bilinear flow, linear flow, and early-time radial flow, while the stress-sensitivity mainly affects the later flow regimes, including intermediate-time pseudoradial flow, pseudo-steady state interporosity flow, and late-time pseudoradial flow. The typical curves will ascend with the increasing of stress-sensitivity coefficient. The research provides a method for precise prediction of formation parameters and has a significant impact on the tight gas reservoir development.

Transient pressure and production dynamics of multi-stage fractured horizontal wells in shale gas reservoirs with stimulated reservoir volume

Multi-stage fracturing in unconventional shale gas reservoirs always creates complex fracture network around horizontal wellbore. The existence of the stimulated reservoir volume (SRV) has significant impact on performance of fractured horizontal well, and various composite models are introduced to simulate gas flow caused by fractured horizontal wells with SRV. However, most of the existing models do not simultaneously taken into account fracture conductivity, non-uniform properties of hydraulic fractures, SRV region, multiple flowing mechanisms of shale gas.This paper extends previous work by presenting a more comprehensive model to simulate the performance of multi-stage fractured horizontal well in shale gas reservoirs. The model takes into account not only the existence of SRV, but also the influence of fracture conductivity, multiple flowing mechanisms (desorption, transient state and pseudo-steady state viscous flow and diffusion) in shale matrix as well as the effect of non-uniform fracture distribution. By employing the source function theory, Laplace transformation and discretization method, a relatively simple semi-analytical solution is obtained. After the verification of the presented model with other published results, the transient pressure and production dynamics are compared and analyzed. The influences of relevant parameters on performance of fractured horizontal wells are also discussed. It is found that the performance of fractured horizontal wells in shale gas reservoirs is mainly affected by the parameters related to SRV (the size of SRV, the density of fractures in SRV, the configuration of primary fractures in SRV), conductivity and distribution of hydraulic fractures, and desorption and diffusion in shale matrix. The model presented in this paper can be easily simplified to simulate simpler cases, such as performance of fractured horizontal wells in tight reservoirs. The model and corresponding conclusions presented in this study will be helpful to understand transient performance of multi-stage fractured horizontal wells in shale gas reservoirs and thus to effectively develop unconventional shale gas reservoirs.