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Keywords: vertical fracture

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Proceedings Papers

Publisher: Society of Petroleum Engineers (SPE)

Paper presented at the SPE Western Regional Meeting, May 27–29, 2010

Paper Number: SPE-132229-MS

... permeability curves show that the oil-water relative permeability not only depends on fluid saturations and flow patterns but also fracture orientation. relative permeability curve flow regime reservoir upstream oil & gas flow orientation

**vertical****fracture**orientation fluid dynamics...
Abstract

Naturally fractured reservoirs contain about 25-30% of the world supply of oil. In these reservoirs, fractures are the dominant flow path. Therefore, a good understanding of transfer parameters such as relative permeability as well as flow regimes occurring in a fracture plays an important role in developing and improving oil production from such complex systems. However, in contrast with gas-liquid flow in a single fracture, the flow of heavy oil and water has received less attention. In this research, a Hele-Shaw apparatus was built to study the flow of water in presence of heavy oil and display different flow patterns under different flow rates and analyze the effect of fracture orientations on relative permeability curves as well as flow regimes. The phase flow rates versus phase saturation results were converted to experimental relative permeability curves. The results of the experiments demonstrate that, depending on fracture and flow orientation, there could be a significant interference between the phases flowing through the fracture. In contrast with other studies, the results also reveal that both phases can flow in both continuous and discontinuous forms. The relative permeability curves show that the oil-water relative permeability not only depends on fluid saturations and flow patterns but also fracture orientation.

Proceedings Papers

Publisher: Society of Petroleum Engineers (SPE)

Paper presented at the SPE California Regional Meeting, April 2–4, 1986

Paper Number: SPE-15116-MS

... relative to the reservoir height, the initial radial flow period ends rapidly and transient pressure behavior becomes identical to that of a uniform flux

**vertical****fracture**. The pressure transient response for multiple drainholes is identical to the single drainhole solution if dimensionless variables...
Abstract

SPE Members Abstract Drainholes have been drilled in several areas of the world and there is a need to understand these drainage systems for accurate well test analysis. This study presents an analytical solution for the transient pressure response of a uniform flux horizontal drainhole in an anisotropic reservoir of finite thickness. The solution also applies for a reservoir with multiple drainholes in a vertical array. The solution shows that there are two possible types of transient pressure behavior depending on the length of the drainhole relative to the height of the reservoir. If the drainhole is short, initial radial flow perpendicular to the drainhole axis is followed by a transition to a perpendicular to the drainhole axis is followed by a transition to a pseudo-radial flow period. If the drainhole length is long relative to pseudo-radial flow period. If the drainhole length is long relative to the reservoir height, the initial radial flow period ends rapidly and transient pressure behavior becomes identical to that of a uniform flux vertical fracture. The pressure transient response for multiple drainholes is identical to the single drainhole solution if dimensionless variables are defined relative to the number of drainholes. Consequently, the pressure response of a uniform flux vertical fracture can also be pressure response of a uniform flux vertical fracture can also be approximated by a vertical array of drainholes. The pressure response for infinite conductivity drainholes is also suggested by analogy to the infinite conductivity vertical fracture solution. Log-log type curves are presented for various drainhole radii and can be used in the conventional manner to determine reservoir characteristics including directional permeability or drainhole half length. Short and long time approximations are presented along with appropriate time limits. Finally, conditions for greater productivity than with vertical wells or hydraulic fractures are presented. Introduction Drainholes are horizontal bores drilled from a vertical wellbore to increase production. The purpose of this study is to present a means for understanding these systems using, pressure transient analysis. Recently, many applications of horizontal drainholes have been attempted or suggested. This increased popularity is due mainly to attractive economics and better drilling technology.' Applications for drainholes includes: productivity index increases, injectivity index increases, greater sweep efficiencies by line flooding from one drainhole to another, water and gas coning reductions, penetration of narrowly missed target zones, intersection of naturally penetration of narrowly missed target zones, intersection of naturally occurring vertical fractures and reduced wellbore damage. The available drainhole literature can be categorized by areas of operational feasibility, productivity increases, and EOR applications. The operational feasibility literature documents the development of flexible drill collars with better directional drilling. These technological advances have reduced the amount of risk involved in drilling horizontal drainholes. Areas of the world where horizontal bores have been drilled with positive results include California Texas, France, Italy and the USSR. The first studies on drainhole productivity using potentiometric models were presented in the mid-1650's by Perrine, Roemershauser and Hawkins, and Landrum and Crawford. These three studies concluded that (1) drainhole length is of primary importance to productivity, (2) additional drainhole footage is more effective on a single well than are additional drainholes, and (3) increases in productivity are proportional to the combined length of all drainholes in the system until a point is reached were additional benefit per added foot begins to diminish. The conclusions of these reports are explained by the drainhole pseudo skin factor presented in this study. Publications have been presented in the early 1980's that give analytical expressions and field results for determining expected productivity increases. The studies showed that horizontal bores productivity increases. The studies showed that horizontal bores were most advantageous for: – tight reservoirs, specially if vertical fractures are suspected – thin beds – thin oil columns or a small density difference between water and oil – soft formations such as chalk that are likely to collapse The third area of drainhole literature is EOR applications of drainholes. The primary work in this area is from Canadian production of heavy crudes. Suggested or applied uses include production of heavy crudes. Suggested or applied uses include continuous steam injection, cyclic injection production techniques, production of tight chalk formations and gravity drainage of production of tight chalk formations and gravity drainage of steam-heated oil through parallel drainholes. Although no published studies on the pressure transient analysis of horizontal drainholes currently exist, several studies in the pressure transient analysis literature are applicable to this study. pressure transient analysis literature are applicable to this study. First is the partially-penetrating uniform flux fracture solution presented analytically by Raghavan et al. The general vertical fracture solution presented analytically for infinite conductivity and uniform flux fractures by Gringarten et al. will be used to find similarities with the horizontal drainhole pressure transient response. A third study of interest is the pressure transient response for a slanted wellbore presented by Cinco. Limiting cases of these three studies approximate the drainhole case and can be used for checking the drainhole solution. P. 215

Proceedings Papers

Publisher: Society of Petroleum Engineers (SPE)

Paper presented at the SPE California Regional Meeting, April 2–4, 1986

Paper Number: SPE-15050-MS

... temperature profile thermal diffusivity

**vertical****fracture**saturation stimulation sagd SPE Society of Petroleum Engineers SPE 15050 Interpretation of Temperature Profiles From the Steam-Stimulated Cold Lake Reservoir by E. Vittoratos, Esso Resources Canada Ltd. SPE Member Copyright 1986, Society...
Abstract

SPE Member Abstract Steam stimulation of the Cold Lake bitumen reservoir causes fracturing of the formation. Steam enters via convection along the fracture plane, and heat propagates perpendicular to this plane by conduction, which in some cases may be enhanced by convection. Temperature profiles from observation wells located around stimulated wells directly give the energy distribution at those locations. The analysis can be extended beyond energy distribution by distinguishing regions of convective and conductive heat transfer in the temperature profiles. Simple analytical models can then yield important insights into the cyclic steam stimulation process, such as fracture geometry and fluid flow velocity. Eight field cases are discussed representing profiles from the injection, shut-in, and production phases of the process. Introduction The Cold Lake oil sands deposit is a major accumulation of bitumen of Cretaceous age, located 300 km northeast of Edmonton, Alberta. Approximately 25 billion cubic metres of bitumen is buried at depths ranging from 300 to 600 m. In the last two decades, commercial in situ steam stimulation recovery techniques have been developed by Esso Resources Canada Limited via several experimental pilots. Pilot operations have been previously summarized. The recovery of the bitumen from the Cold Lake deposits faces three major challenges: high bitumen viscosity, low reservoir injectivity, and low reservoir energy. The bitumen's viscosity is highly dependent on temperature, and by steam injection it can be lowered to low values with an energy expenditure that represents only a small fraction of the energy content of the formation at typical bitumen saturations. But the low injectivity necessitates fracturing of the formation in order that commercial rates of steam injection can be achieved. The energy distribution and bitumen depletion will follow the fracture trends, and conformance problems can be anticipated. Even with a lowered viscosity, movement of the bitumen to the wellbore can be difficult because of the low reservoir energy; in fact, some of the proposed recovery processes for the Cold Lake sands assume that gravity is the predominant driving force. The evolution of understanding in steam stimulation techniques has been essentially empirical. Alternative operating procedures such as perforating depth - have been tested via pilot operations. More than 50 observation wells have played an important role in the evaluations of pilot performance. This paper deals with the interpretation of the temperature profiles obtained from these observation wells. Temperature observation wells are often placed in thermal pilots. The temperature profiles obtained directly represent the injected energy distribution at the well locations. Various thermal efficiency parameters can then be estimated, such as the percent energy remaining in the target interval. However, the percent energy remaining in the target interval. However, the interpretation of the temperature profiles from observation wells has not been directly addressed in the literature, but is referred to in the context of other deliberations. P. 19

Proceedings Papers

Publisher: Society of Petroleum Engineers (SPE)

Paper presented at the SPE California Regional Meeting, April 11–13, 1984

Paper Number: SPE-12743-MS

... Abstract The effect of the partial penetration of an infinite conductivity fracture on the transient pressure behavior of a

**vertically****fractured**well is investigated. Analysis of results shows that the pressure behavior of a well intersected by a partially-penetrating infinite conductivity...
Abstract

Abstract The effect of the partial penetration of an infinite conductivity fracture on the transient pressure behavior of a vertically fractured well is investigated. Analysis of results shows that the pressure behavior of a well intersected by a partially-penetrating infinite conductivity vertical fracture can be divided into three flow periods: the early time flow period which is characterized by a formation linear flow as in the case of a fully-penetrating infinite-conductivity vertical fracture, the infinite-acting flow period and the pseudoradial flow period which develops after the effects of the vertical boundaries of the reservoir are felt in the pressure behavior of the well. A log-log graph of log(hf/h)pWD versus log t shows a slope of one half during the early time, flow period of a well with an infinite-conductivity period of a well with an infinite-conductivity partially penetrating fracture. The time for the end of the partially penetrating fracture. The time for the end of the early time flow period is directly related to the square of the dimensionless height of the fracture, hfd which is defined as the ratio between the height of the fracture and its half length. This time becomes so small for small values of hfD that the linear formation flow period will not show up for practical purposes. The solutions during the infinite-acting flow period are, for the different values of penetration period are, for the different values of penetration ratio and a given value of characterized by a single envelope curve in the log-log graph previously mentioned. The time for the start of the pseudoradial flow period shows no dependence on the penetration ratio and period shows no dependence on the penetration ratio and on the dimensionless fracture height except for fractures with dimensionless heights larger than about 1 and penetration ratios smaller than 1/5. Even though solutions were mainly obtained for the case of a fracture located at the middle of the formation, the effect of offsetting the fracture was investigated for some particular cases. As expected, the solutions are the same up to the end of the infinite acting flow period which slightly varies as a function of the fracture location. The solutions are presented in the form of type curves suitable for transient pressure analysis procedures. procedures Introduction Most of the work done on the behavior of fractured wells have considered a totally-penetrating fracture and only a few studies have dealt with the effects of a partially-penetrating fracture. partially-penetrating fracture. Tinsley et al. used an electrolytic model to deter mine the effect of the height of the fracture on the production of a well intersected by a finite- production of a well intersected by a finite- conductivity vertical fracture under steady-state conditions. Cinco derived an analytical solution for the unsteady-state distribution created by a well intersected by a partially-penetrating uniform-flux inclined fracture in an infinite slab reservoir. An expression for the pseudo-skin factor was derived as well, based on a late time approximation to the solution. No further analysis was however presented. Raghavan et al. investigated the effect of the partial penetration of a vertical fracture on the partial penetration of a vertical fracture on the transient pressure behavior of a fractured well. A uniform flux across the fracture was assumed, for which case an analytical solution was possible. An approximate solution for the transient pressure behavior well with a partially-penetrating infinite- conductivity fracture was obtained by evaluating the uniform flux solution at a point in the fracture which was assumed to yield the infinite-conductivity solution. This approximation was an extension of the relations between the infinite and uniform-flux solutions previously found by Gringarten et al., in the case of a previously found by Gringarten et al., in the case of a totally-penetrating vertical fracture, and by Muskat in the case of steady-state flow towards a partially-penetrating well. The solution to the partially- partially-penetrating well. The solution to the partially- penetrating infinite-conductivity problem would have required penetrating infinite-conductivity problem would have required however of a semi-analytical type of solution. Mao studied the productivity of vertically fractured wells using a potentiometric model. Finite conductivity and partial penetration were considered. It is the purpose of this paper to formulate and to solve properly the unsteady-state flow problem to a well with an infinite-conductivity partially- penetrating fracture and to present the results in a suitable penetrating fracture and to present the results in a suitable form for fracture design and evaluation procedures. P. 163

Proceedings Papers

Publisher: Society of Petroleum Engineers (SPE)

Paper presented at the SPE California Regional Meeting, April 18–20, 1979

Paper Number: SPE-7983-MS

... Drillstem Testing numerical approach hydraulic fracturing analytic solution data mining drillstem/well testing Upstream Oil & Gas

**vertical****fracture**assumption Narasimhan Storativity Simulation cr 100 wellbore storage correspond conductivity reservoir subdomain fracture...
Abstract

Abstract A numerical method, based on an Integral Finite Difference approach, is presented to investigate wells intercepting fractures in general and vertical fractures in particular. Such features as finite conductivity, wellbore storage, damage, and fracture deformability and its influence as permeability are easily handled. The advantage of the numerical approach is that it is based on fewer assumptions than analytic solutions and hence has greater generality. Illustrative examples are given to validate the method against known solutions. New results are presented to demonstrate the applicability of the method to problems not apparently considered in the literature so far. Introduction The problem of fluid flow to a well intercepting a single vertical fracture H of considerable interest in the field of petroleum engineering. The transient pressure response of such a well to fluid production has been investigated by previous workers production has been investigated by previous workers using analytical solutions, some of which are evaluated numerically. Despite their power, analytical methods have certain limitations. To overcome these limitations, numerical methods in conjunction with fast computing devices can be utilized with great advantage. The purpose of this paper is to describe and demonstrate the power of a fairly general numerical model in studying fluid flow to a well intercepting a vertical fracture. The Problem The problem of interest is schematically represented in Fig. 1. The reservoir is assumed to be homogeneous, horizontal, a really infinite and of thickness h. A vertical fracture of width w, length 2Xf and extending, throughout the thickness of the reservoir and is fully penetrated by a well of radius rw. It is assumed that the well produces fluid at a prescribed (usually constant) rate. The problem is to predict the pressure transient problem is to predict the pressure transient behavior of the system. in general and the well in particular. particular. Previous Work Previous Work Although interest in wells intercepting vertical fractures dates back to 1960, the first comprehensive study of the pressure transient response of such a well was performed by Gringarten et all who studied the case of flow to an infinitely conducting vertical fracture, with a hypothetical zero-radius well at its center. This and a few subsequent studies considered not only an infinite reservoir but also various types of bounded reservoirs. Later, Cinco-Ley et al extended the Green's functions approach of Gringarten et all to consider the mare realistic cases of finite conductivity vertical fractures. In their studies, Cinco-Ley et al coupled the Green's fraction solution of the earlier work with a one dimensional, linear solution for fluid flow within the fracture, the coupling procedure being subject to continuity of fluxes at the procedure being subject to continuity of fluxes at the fracture surface. To evaluate their solutions, Cinco-Ley et al used a numerical method. In subsequent studies, Cinco-Ley and Samaniego extended the solutions to include effects of wellbore storage and formation damage around the fracture. Although they do discretize the fracture into several segments in their numerical evaluation, Cinco-Ley et al's method is basically analytic or at best semi-analytic in nature. Limitations of Analytic Approach Use analytic approach has formed the backbone of well test interpretation and reservoir analysis since the 30's and has provided innumerable valuable insights in understanding reservoir response. Yet, tractable analytic solutions can be obtained only if the system under consideration is simple.