Pressure Behavior Of Horizontal Wells Research Articles

Multiphase transient analysis of horizontal wells during CO2-EOR

We apply a numerical well test model that considers the transient flow in well and the complex displacement mechanisms for the multiphase transient analysis of horizontal wells during CO 2 -EOR. Aimed to perform a systematic and reliable analysis, we run the model on a high-resolution non-uniform grid to accurately capture the transient flow in the near wellbore region as well as the complex displacement process. In this work, we interpret the pressure response curve in two steps to find the root causes of the particular transient behaviors. First, we identify five typical flow regimes through the traditional pressure transient analysis method for horizontal wells which gives us a basic understanding of the characteristics of the pressure response curve. Second, assisted with the corresponding analysis method, we figure out the durations on the curve that correspond to different component banks. By taking the complex displacement mechanisms into consideration, we find that the component banks have a large influence on the curve and identify the root cause of each unique characteristic. Besides, we conduct a systematic sensitivity analysis with respect to multiple parameters such as miscible condition, wellbore storage coefficient, skin factor, horizontal well length, anisotropy, and amount of injected CO 2 . Finally, we have a better understanding of the transient pressure behavior of horizontal wells during CO 2 -EOR, find a way to determine the miscibility underground, and feel more confident in applying the pressure transient data for analysis and parameter estimation. • The EoS based compositional model and wellbore storage model are coupled in a fully-implicit parallel reservoir simulator. • A new interpretation method is proposed for the pressure transient analysis of horizontal wells during CO 2 -EOR. • The effects of flow patterns and complex displacement mechanisms on transient behavior are analyzed in detail. • The results point out a cheap and reliable way to monitor the CO 2 displacement process in horizontal well patterns.

Transient pressure behavior of horizontal well in gas reservoirs with arbitrary boundary

Transient pressure analysis is a crucial tool to forecast the production performance during the exploration and production process in gas reservoirs. Usually, a regular shaped outer boundary is assumed in previous studies for well-testing analysis, which is just a simplification of practical cases and cannot reflect the actual boundaries of reservoirs. In this paper, a mathematical model is established to analyze the transient pressure behaviors of a horizontal well in an arbitrarily shaped gas reservoir. Dimensionless treatment, Laplace transformation, and boundary element method are applied in solving the model, which is verified by comparing with the results from the source function method. Based on the Stehfest numerical inversion method, the models of single-porosity media and dual-porosity media are solved respectively. Then, the time-domain curves of pseudo pressure and its derivative are obtained, and the flow regimes are identified. Finally, the impacts of some critical parameters on pressure transient behaviors are analyzed, including storativity ratio, interporosity coefficient, well length, and well orientation. This paper presents an effective way to handle complex external boundary problems in gas reservoirs.

Semi-analytical model of the transient pressure behavior of complex fracture networks in tight oil reservoirs

Unconventional resources have been successfully exploited with technological advancements in horizontal drilling and multi-stage hydraulic fracturing, especially in North America. Due to pre-existing natural fractures and the presence of stress isotropy, several complex fracture networks can be generated during fracturing operations in unconventional reservoirs.Based on Ozkan's plane source function, by virtue of equivalent conversion and coordinate transformation, a new plane source function was derived that can handle the fluid flow behavior in an inclined fracture in dual media, anisotropic, tight oil reservoir. Using the superimposing method, a semi-analytical model was established to analyze the transient pressure behavior of horizontal wells with complex fracture networks. Using this method, we defined five flow regimes: Linear flow, fractures interference flow, first radial flow, cross flow andpseudo-radial flow. The influences of some of the critical parameters on the transient pressure behavior were studied, including the fracture number, distribution of the fractures, storage ratio, and so on.This paper provides a useful tool for reservoir engineers regarding fracture design as well as for estimating the performance of horizontal wells with complex fracture networks.

New approach for describing transient pressure response generated by horizontal wells of arbitrary geometry

This paper is aimed at developing a methodology for studying the transient pressure behavior of horizontal wells with any curvilinear trajectory in an isotropic/anisotropic arbitrarily shaped reservoir. This methodology employs generalized functions to represent the tortuous horizontal well. A particular way of removing the singularities involved in the partial differential equation is based on reducing the original problem to the conventional solution of the homogeneous diffusivity equation under any given initial and boundary conditions. The Green function method and any standard numerical technique are combined in a single computational strategy to obtain the transient pressure response generated by a curved and twisted horizontal well in reservoirs with irregular boundaries. Analytical methods can be also used, whenever possible, to solve the reduced problem. This proposal can be easily broadened to analyze the performance of the pressure transient of any kind of reservoir sources or sinks that can be modeled using generalized functions. Some models are presented.

Pressure Behavior of Horizontal Wells in Multilayer Reservoirs With Crossflow

Summary New analytic solutions for horizontal wells with wellbore storage and skin in layered reservoirs with crossflow are presented. These layered systems can be bounded by two horizontal impermeable boundary planes at the top and the bottom, or either one of the boundary planes can have a constant pressure (the system either has a gas cap or an active aquifer), while the other is maintained as a no-flow boundary. The new solutions are derived by utilizing the reflection and transmission concept of electromagnetics to solve fluid flow problems in three dimensional layered reservoirs, where non-homogeneity is in only one direction. The solution technique is sufficiently general that it may be applied to a wide variety of fluid flow and well testing problems involving single-phase flow. The solutions are applied to a number of layered-reservoir examples. It is shown that a gas cap or aquifer should automatically not be treated as a constant-pressure boundary. It is also shown that estimation of layer parameters from conventional well tests is difficult. A field example is presented for the use of the new solutions for the interpretation of a buildup test from a horizontal well in a multilayer reservoir, where the layers are separated sporadically by low permeability zones. The Horner method is also used to interpret the field test; however, Horner does not work well for layered systems with horizontal wells.

Well Testing and Interpretation for Horizontal Wells

The use of transient well testing for determining reservoir parameters and productivity of horizontal wells has become common because of the upsurge in horizontal drilling. Initially, horizontal well tests were analyzed with the conventional techniques designed for vertical wells. During the last decade, analytic solutions have been presented for the pressure behavior of horizontal wells. New flow regimes have been identified, and simple equations and flow regime existence criteria have been presented for them. The flow regimes are now used frequently to estimate horizontal and vertical permeabilities of the reservoir, wellbore skin, and reservoir pressure. Although the existing tools and interpretation techniques may be sufficient for simple systems, innovation and improvement of the present technology are still essential for well testing of horizontal wells in many reservoirs with different geological environments and different well-completion requirements.