Pressure Transient Behavior of Horizontal Wells Intersecting Multiple Hydraulic and Natural Fractures in Conventional and Unconventional Unfractured and Naturally Fractured Reservoirs

Abstract

Faults and fractures are common features in many well-known reservoirs. In many of these reservoirs, horizontal wells are drilled to intersect a large number of fractures, particularly in low-matrix-permeability formations. In addition, the application of horizontal wells intersecting multiple hydraulic fractures has been widespread to allow shale gas and oil reservoirs, some of which are also naturally fractured, to produce economically. In this paper, we investigate the pressure transient behavior of horizontal wells in continuously and discretely naturally fractured reservoirs (NFR)s using semi-analytical boundary element solutions. These solutions have the advantages of the absence of grids and reduced dimensionality. Furthermore, they provide continuous rather than discrete solutions. The solutions are sufficiently general to be applied to many different well geometries and reservoir geological settings, where the spatial domain may include arbitrary fracture and/or fault distributions with different types of outer boundaries. A number of solutions have been published in the literature for horizontal wells in NFRs using the conventional dual-porosity models that are not applicable to many of these reservoirs. Most of these published solutions ignore the wellbore and the unfractured sections of the horizontal well. Therefore, they cannot capture the true early-time response, such as fracture radial flow. They may also yield incorrect damage skin values. Our solutions take these effects into account. Our solutions can also be applied to shale gas and oil reservoirs without shale-gas transport nonlinearities when the average reservoir pressure is above the desorption pressure. Our solutions for horizontal wells in fractured reservoirs can contain any spatial distribution of finite or infinite conductivity fractures with arbitrary length and orientation. The number and type of fractures (hydraulic or natural) intersecting the wellbore and with each other are not limited in both homogeneous and naturally fractured reservoirs. We present a number of examples to show different flow regimes that a horizontal well with multiple fractures exhibits, and to show that the conventional dual-porosity models simply do not work and can be deceptive. In our solutions, continuous and discrete conductive and nonconductive fractures are treated explicitly. The exact treatment of the uniform wellbore pressure condition, and the inclusion of the wellbore and the unfractured sections of the horizontal well have led to identification of new flow regimes that were not apparent from the existing solutions. Consequently, our solutions capture the true pressure transient behavior of the system, such as fracture radial flow. In this paper, a new classification of wellbore and fracture skin damage is given, and their effects on the pressure transient behavior are investigated. There are many factors that dominate the pressure transient behavior of horizontal wells intersected by multiple hydraulic fractures in naturally fractured reservoirs, such as fracture conductivities, lengths, and distributions, as well as whether or not fractures intersect the wellbore. Diagnostic derivatives plots are presented for a variety of horizontal wells with multiple fractures in homogenous and NFRs. It is shown that these reservoirs exhibit many different flow regimes. A multistage-fractured horizontal well in a very low-permeability shale reservoir example is also presented. Finally, we have presented two field buildup test examples from NFRs

Seepage Model and Pressure Response Characteristics of Non-Orthogonal Multi-Fracture Vertical Wells with Superimposed Sand Body in Tight Gas Reservoirs

“…At present, many scholars have studied the seepage model of fractured wells in tight reservoirs. Zerzar and Bettam [11] combined the boundary element method and integral transformation method to provide analytical solutions for multi-stage fractured horizontal wells in semi-infinite or anisotropic closed reservoirs. Further, Li [12] used point source function, Green function, Fourier and Laplace transform methods to give the formula of unstable pressure for multi-stage fractured horizontal wells with infinite conductivity and took into account the influence of fracture wall pollution and wellbore storage on the unstable pressure.…”

Integro-Differential Solutions for Formation Mechanical Damage Control During Oil Flow in Permeability-Pressure-Sensitive Reservoirs

“…In any case, the formulation proposed did not approach stress-sensitive responses, as well as the role of the source/sink term in the final solution of the NHDE. Kuchuk & Biryukov (2013), Kuchuk, Morton & Biryukov (2015), Kuchuk, Morton & Biryukov (2016) investigated the rate and pressure-transient behavior of multistage fractured horizontal wells in conventional and unconventional homogeneous and naturally fractured reservoirs, the latter of which can contain any spatial distribution of finite or infinite-conductivity fractures of arbitrary length and orientation. The number and type of fractures (hydraulic or natural) intersecting the wellbore and self-intersecting were unlimited.…”