This mathematical model of the mechanics of flow of wet and saturated steam down the wellbore during steam injection takes into account the variation of steam temperature and pressure due to friction, as well as heat losses by radiation, conduction, and convection. It consists of two coupled nonlinear equations that are solved iteratively. Introduction Chekalyuk et al., Moss and White, and Fokeev and Kepyrin, investigated wellbore heat losses during injection of a hot or cold fluid down the casing. Ramey made a comprehensive study of the injection of liquids and gases down casing or tubing. Squier et al. presented a complete analytical treatment of hot water injection down the wellbore. Satter extended Ramey's treatment to the case of steam injection. Huygen and Huitt, presented results of a theoretical and experimental treatment of wellbore heat losses during steam injection, and pointed out the importance of the radiation heat loss. Holst and Flock as well as Earlougher extended the above treatments by including, steam pressure calculations. Eickmeier et al. considered the early transient performance, using a finite-difference model. performance, using a finite-difference model. Apart from these studies, Leutwyler gave a comprehensive treatment of casing temperature behavior, and Willhite presented a complete calculation of the over-all heat presented a complete calculation of the over-all heat transfer coefficients. The chief objective of our work was to formulate a comprehensive mathematical model of steam injection into a reservoir to include simultaneous calculation of steam pressure and quality. The model took into account the variation of steam temperature and pressure due to friction, as well as heat losses by pressure due to friction, as well as heat losses by radiation, conduction, and convection, and consisted of two coupled nonlinear differential equations that were solved iteratively. The model results were compared with those predicted by several of the above-mentioned approaches. Formulation of the Model Steam at a constant injection pressure, constant mass flow rate, and constant quality (at the surface) is injected through the tubing into the wellbore. The complete system consists of the fluid, the tubing, the annular space containing low-pressure air, the casing, the cement, and the formation. We propose to compute the pressure and the quality of steam as functions of depth and time. An energy balance and a momentum balance can be written for the flowing fluid as follows: Energy balance ..........(1) Momentum balance ..............................(2) The term dQ is given by,...................(3) where the rate of heat transfer to the formation is (4) dq  =  , JPT P. 139

The full potential of a well cannot be ascertained if the proppant is not cleaned up properly after a fracture treatment, particularly in tight gas formations. This paper makes an in-depth evaluation of the impact of fracturing water that remains trapped and unproduced within the proppant pack. This water must be differentiated from the condensed water or water from the reservoir that may be produced. The paper studies some of the main fracturing and reservoir characteristics and identifies variables that have a major impact in reducing the proppant pack conductivity and well production. The major variables studied and analyzed are the fracture fluid and broken gel viscosity, the proppant material, closure stress, fracture conductivity, reservoir pressure, and formation permeability. The paper presents an approach to evaluate and correlate different fracture and reservoir variables to the post-fracture sustained production rate. The study was conducted in two steps; first is a sensitivity study using a full scale numerical simulator and using important reservoir properties from a particular gas field in Saudi Arabia along with the characteristics of typical fluids and proppants pumped during a multistage fracturing treatment in horizontal wells in a low permeability sandstone reservoir. The second step consisted of analyzing the actual post-frac water recovery, test gas rate, and long-term production performance. Comparisons are drawn to establish the variables that impact well productivity the most.The paper presents important plots to illustrate the flow back behavior and well productivity under different fracturing fluids scenarios. There have been practical steps taken to minimize fracture damage, thereby maximizing well deliverability. The factor impairing deliverability the most is the unbroken gel viscosity. The early time production behavior is a function of broken gel and fracture conductivity. With the improved treatment scheduling, use of better fluids and proppants, and application of novel completion methods, the well performances have been significantly improved in challenging, heterogeneous, and low permeability reservoirs.

This paper was prepared for presentation at the SPE Unconventional Resource s Conference and E xhibition-A sia P acific held in B risbane, A ustralia, 11-13 Novem ber 2013.This paper was selected for presentation by an S P E program com m ittee following review of inform ation contained in an abstract subm itted by the author(s). Contents of the paper have not been reviewed by the S ociety of P etroleum E ngineers and are subject to correction by the author(s). The m aterial does not necessarily reflect any position of the S ociety of P etroleum E ngineers, its officers, or m em bers. E lectronic reproduction, distribution, or storage of any part of this paper without the written consent of the S ociety of P etroleum E ngineers is prohibited. P erm ission to reproduce in print is restricted to an abstract of not m ore than 300 words; illustrations m ay not be copied. The abstract m ust contain conspicuous acknowledgm ent of S P E copyright. AbstractHorizontal wells in low to moderate permeability reservoirs are routinely fractured to obtain higher sustained production. A key element to consider for the success of a fracturing treatment is the optimum placement of multiple fractures in the lateral section. These treatments are known as multi-stage fracturing (MSF) and can generally be placed using open-hole multi-stage fracturing assembly (OHMS) or a more conventional perforate, stimulate, and plug (PSP) option in a cemented liner. This paper illustrates examples of production behavior from numerical modeling of gas wells drilled, completed, and stimulated in high pressure and high temperature environments, in low to moderate permeability reservoirs. Numerous comparisons of production performances modeled using numerical simulator for OHMS and PSP applications with varying reservoir and completion parameters are provided. Examples are depicted to show horizontal well performances and how candidates and completion assemblies are selected to obtain the best production rates. Various subsets of OHMS such as singleport ball drop system per stage, high velocity jetting through coiled tubing to create slots to effectively connect wellbore with the reservoir, and multiple cluster perforation system for limited treatment have all been used in the Saudi Arabian gas reservoirs. PSP method is also being considered and used. The paper refers to the impact of drilling azimuth, well cleanup, and application of polymer-free fluids on well performance. The paper also shows that drilling wells in the minimum stress direction in low permeability gas reservoirs, completing them with multistage fracturing assemblies, and conducting high-volume treatments contribute to sustained long-term productivity.

In this work the fundamentals and theoretical principles are presented that describe a system used for both pressure data acquisition and analysis. The advantages of using equivalent time and pseudo equipment time in the plotting functions used for pressure transient analysis is explained. For pressure data analysis, the system automatically optimizes the reservoir parameters, resulting in a theoretical profile that matches the measured data with minimum standard deviation within the noise band of the measured data. Regarding calculation of reservoir parameters, the system calculates the value of the parameter by non linear regression using the entire test profile. The reservoir models included in the system are described and several field applications are presented. A main result derived from this work is that we can conduct an accurate test faster and reduce rig time using advanced plotting functions and regression techniques. Complex systems like layered reservoirs and horizontal wells can be handled by the system.

In this work, a brief summary is presented on the fundamental principles of multirate testing. The main objective is the analysis of several field cases where the technique has been successfully in the determination of drainage area reserves. The method of solution is presented for pressure transient analysis and involves the use of a numerical simulator in most of the cases for an optimum reservoir modeling. Examples of tests conducted in the Maracaibo Lake fields are presented. Based on several field cases, an efficient design of the multirate test in order to get the reservoir evaluation objectives was obtained. An extended flow rate period was added to the conventional way to conduct these tests resulting in a better reservoir description for the drainage area investigated. The results were used to determine the next development well in the field under study.