The Influence of Vertical Fractures Intercepting Active and Observation Wells on Interference Tests

Abstract This paper reviews pressure behavior at an observation well intercepted by a vertical fracture. The active well was assumed either unfractured or intercepted by a fracture parallel to the fracture at the observation well. We show that a vertical fracture at the observation well has a significant influence on the pressure response at that well, and therefore wellbore conditions at the observation well must be considered. New type curves presented can be used to determine the compass orientation of the fracture plane at the observation well. Conditions are delineated under which the fracture at the observation well may influence an interference test. This information should be useful in designing and analyzing tests. The pressure response curve at the observation well has no characteristic features that will reveal the existence of a fracture. The existence of the fracture would have to be known a priori or from independent measurements such as single-well tests. Introduction In this work, we examine interference test data for the influence of a vertical fracture located at the observation well. All studies on the subject of interference testing have been directed toward understanding the effects of reservoir heterogeneity or wellbore conditions at the active (flowing) well. Several correspondents suggested our study because many field tests are conducted when the observation well is fractured. They also indicated that it is not uncommon for both wells (active and observation) to be fractured. To the best of our knowledge, this is the first study to examine the influence of a vertical fracture at the observation well on interference test data. Two conditions at the active well are examined: an active well that is unfractured (plane radial flow) and an active well that intercepts a vertical fracture parallel to the fracture at the observation well. The parameters of interest include effects of the distance between the two wells, compass orientation of the fracture plane with respect to the line joining the two wellbores, and the ratio of the fracture lengths at the active and observation wells if both wells are fractured. The results given here should enable the analystto interpret the pressure response at the fractured observation well.to interpret the pressure response when both the active and the observation wells are fracturedto design tests to account for the existence of a fracture at one or both wells, andto determine quantitatively the orientation and/or length of the fracture at an observation well. We also show that one should not assume a priori that the effect of a fracture on the observation well response will be similar to that of a concentric skin region around the wellbore-i.e., idealizations to incorporate the existence of the fracture, such as the effective wellbore radius concept, may not be applicable. Mathematical Model and Assumptions In this study, we consider the flow of a slightly compressible fluid of constant viscosity in a uniform and homogeneous porous medium of infinite extent. Fluid is produced at a constant surface rate at the active well. Wellbore storage effects are assumed negligible because the main objective of our work is to demonstrate the influence of the fractures. However, note that wellbore storage effects may mask the early-time response at the observation well. Refs. 1 and 2 discuss the influence of wellbore storage on interference test data. We obtained the solutions to the problems considered here by the method of sources and sinks. The fracture at the observation well was assumed to be a plane source of infinite conductivity. SPEJ P. 933^

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An Analytical Study of Interference in Composite Reservoirs

Society of Petroleum Engineers Journal ◽

10.2118/10902-pa ◽

1985 ◽

Vol 25 (02) ◽

pp. 281-290 ◽

Cited By ~ 8

Author(s):

Abdurrahman Satman

Keyword(s):

Pressure Drop ◽

Composite System ◽

Pressure Response ◽

Oil Field ◽

Observation Well ◽

Wellbore Storage ◽

Interference Test ◽

Interference Tests ◽

Inner Region ◽

Observation Wells

Satman, Abdurrahman; SPE; Technical U. of Istanbul Abstract This paper discusses the interference test in composite reservoirs. The composite model considers all important parameters of interest: the hydraulic diffusivity, the mobility ratio, the distance to the radial discontinuity, the distance between wells, the wellbore storage, and skin effect at the active well. Type curves expressed as a function of proper combinations of these parameters are presented. Introduction Interference tests are widely used to estimate the reservoir properties. An interference test is a multiwell test that requires at least one active well, either a producer or injector, and at least one observation well. During the test, pressure effects caused by the active well are measured at the shut-in observation wells. Basic techniques for analyzing interference tests in uniform systems are discussed in Ref. 1. Usually, type-curve matching is the preferred technique for analyzing the pressure data from the test. Early interference test studies assumed that the storage capacity of the active well and the skin region around the sandface have a negligible effect on the observation well response. Recently, investigators have focused on wellbore storage and skin effects. Tongpenyai and Raghavan presented a new solution for analyzing the pressure response at the presented a new solution for analyzing the pressure response at the observation well, which took into account the effects of wellbore storage and skin at both the active and the observation wells. They produced type curves expressed as a function of exp(2S) products, the ( / ) ratios, and ( / ) to correlate the pressure response at the observation well. Composite systems are encountered in a wide variety of reservoir situations. In a composite system, there is a circular inner region with fluid and rock properties different from those in the outer region. Such a system can occur in hydrocarbon reservoirs and geothermal reservoirs. The injection of fluids during EOR processes can cause the development of fluid banks around the injection wells. This would be true in the case of a in-situ combustion or a steamflood. In a geothermal reservoir, pressure reduction in the vicinity of the well may cause the phase boundaries. A producing well completed in the center of a circular hot zone surrounded by producing well completed in the center of a circular hot zone surrounded by a concentric cooler water region is also a composite system. During the early to late 1960's, there was great interest in the composite reservoir flow problem. Hurst discussed the "sands in series" problem. He presented the formulas to describe the pressure behavior of problem. He presented the formulas to describe the pressure behavior of the unsteady-state flow phenomenon for fluid movement through two sands in series in a radial configuration, with each sand of different permeability. Mortada studied the interference pressure drop for oil fields located in a nonuniform extensive aquifer comprising two regions of different properties. He presented an expression for the interference pressure drop properties. He presented an expression for the interference pressure drop in an oil field resulting from a constant rate of water influx in another oil field. Loucks and Guerrero presented a qualitative discussion of pressure drop characteristics in composite reservoirs. Ramey and Rowan and pressure drop characteristics in composite reservoirs. Ramey and Rowan and Clegg developed approximate solutions. Refs. 11 through 13 also discuss composite reservoir systems and present either analytical or numerical solutions. Composite system model solutions have been used to determine some critical parameters during the application of EOR processes. The formation of a fluid bank around the injection well makes the reservoir a composite system. Van Poollen and Kazemi discussed how to determine the mean distance to the radial discontinuity in an in-situ combustion project. Refs. 16 and 17 discuss the effect of radial discontinuity in interpretation of pressure falloff tests in reservoirs with fluid banks. Sosa et al. examined the effect of relative permeability and mobility ratio on falloff behavior in reservoirs with water banks. The presence of different temperature zones in nonisothermal reservoirs may resemble permeability boundaries during well testing. Mangold et al. presented a numerical study of a thermal discontinuity in well test analysis. Their results indicated that nonisothermal influence could be detected and accounted for by tests of sufficient duration with suitably placed observation wells. Horne et al. indicated the possibility of determining compressibility and permeability contrasts across the phase boundaries in geothermal reservoirs. The most recent study of well test analysis in composite reservoirs was by Eggenschwiler, Satman et al. Their studies presented a very general composite system model. The problem was solved analytically by using the Laplace transformation with numerical inversion. The solution concerned the transient flow of a slightly compressible fluid in a porous medium during injection or falloff for a single well confined in concentric regions of differing mobilities and hydraulic diffusivities. The system assumed both wellbore storage and a skin effect. Their results indicated that a pseudosteady-state pressure response exists in the transition region between the inner region and outer region semilog straight lines. This response is drawn on a Cartesian vs. plot, the slope of which is used to estimate the bulk volume of the inner region. SPEJ p. 281

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Pressure Response at Observation Wells in Fractured Reservoirs

Society of Petroleum Engineers Journal ◽

10.2118/10839-pa ◽

1984 ◽

Vol 24 (06) ◽

pp. 628-638 ◽

Cited By ~ 5

Author(s):

C.C. Chen ◽

N. Yeh ◽

R. Raghavan ◽

A.C. Reynolds

Keyword(s):

Fractured Reservoirs ◽

Pressure Response ◽

Fracture System ◽

Unsteady State ◽

Fractured Reservoir ◽

Observation Well ◽

Naturally Fractured ◽

The Matrix ◽

Interference Test ◽

Observation Wells

Abstract This work examines interference test data in a naturally fractured reservoir. The reservoir model examined here assumes that the reservoir can be represented by a system of horizontal fractures that are separated by the matrix. This model is identical to the deSwaan-Kazemi model. The main contribution of our work is that we combine the parameters of interest in a simple way and present solutions that can be used directly for field application. These solutions can be used to design or analyze interference tests. We also compare the solution for unsteady-state flow in the matrix with the Warren-Root model, which assumes pseudosteady-state fluid flow in the matrix. Introduction This work examines the pressure response at an observation well in a fractured reservoir. Previous works by Kazemi et al. and Streltsova-Adams have examined the pressure response based on the Warren and Root model. In this work, however, we assume unsteady-state fluid transfer from the matrix to the fracture system. We consider the model proposed by deSwaan and Kazemi. This model assumes that the fractured reservoir can be replaced by an equivalent set of horizontal fractures separated by matrix elements (Fig. 1). The results of this study, however, can be applied to other unsteady-state models proposed in the literature. The main contribution of this work is that type curves convenient for analyzing data are presented. We have combined the parameters of interest and correlated results in terms of dimensionless groups that are commonly used in well test analysis. A comprehensive discussion of the pressure behavior at an observation well in a fractured reservoir is presented. Procedures to analyze data by conventional semilog methods also are discussed. New observations on the pressure response at an observation well are presented. For purposes of comparison, we also examined the pressure response in a reservoir that obeys the Warren and Root idealization. Assumptions and Mathematical Model The mathematical model considered here assumes the flow of a slightly compressible (of constant viscosity) fluid in a naturally fractured reservoir. We assume that the matrix-fracture geometry is as shown in Fig. 1. Individually, the fractures and the matrix are assumed to be homogeneous, uniform, and isotropic porous media with distinct properties. Gravitational forces are assumed negligible. The reservoir is assumed to be infinitely large-i.e., the outer boundaries have no effect on the pressure response. The initial condition assumes that the pressure is constant at all points in the reservoir. We assume that the flowing well produces at a constant rate and that the two wells both penetrate the fracture system. In addition, we impose four fundamental assumptions:all production is from the fracture system,flow in the matrix system is one-dimensional-i.e., in the z direction (see Fig. 1),flow in the fracture system is radial, andboth the producing and observation wells are line source wells and wellbore storage and skin effects are neglected. Assumptions 1, 2, and 3 have been used extensively in previous studies of naturally fractured reservoirs. Recent results of Reynolds et al. indicate that these assumptions are valid for the model considered in Fig. 1 if the flow capacity of the matrix system is small relative to the flow capacity of the fracture system (see Ref. 9 for specific details). Assumption 4 is used in virtually all studies of interference testing. (A comprehensive discussion of the influence of wellbore storage and skin effects on interference test data is given in Refs. 10 and 11.) It is important to realize that flee preceding four assumptions (see 2 in particular) imply that the pressure response at the observation well will be equal to the pressure response in the fracture system at the point where the observation well intersects the fractured system. All results given in this study are based on dimensionless variables for purposes of convenience. The dimensionless variables are defined as follows. The dimensionless pressure drop in the reservoir is ...............(1) Here, is the permeability of the fracture system and is the total thickness of the fracture system. If the model of Fig. 1 contains horizontal fractures, then = where is the thickness of each horizontal fracture. The term represents the surface flow rate, is the formation volume factor, is the viscosity of the fluid, and ( ) is the pressure at point at time . The subscript f refers to the fracture. All quantities are expressed in SPE-preferred SI metric units. SPEJ P. 628^

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Analysis of Interference Test Data Influenced by Wellbore Storage and Skin at the Flowing Well

Journal of Petroleum Technology ◽

10.2118/8029-pa ◽

1980 ◽

Vol 32 (01) ◽

pp. 171-178 ◽

Cited By ~ 15

Author(s):

Wei Chun Chu ◽

J. Garcia-Rivera ◽

Raghavan Rajagopoal

Keyword(s):

Test Data ◽

Wellbore Storage ◽

Interference Test ◽

Flowing Well

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The Effect of Wellbore Storage and Skin on Interference Test Data

Journal of Petroleum Technology ◽

10.2118/8863-pa ◽

1981 ◽

Vol 33 (01) ◽

pp. 151-160 ◽

Cited By ~ 30

Author(s):

Y. Tongpenyai ◽

Rajagopal Raghavan

Keyword(s):

Test Data ◽

Wellbore Storage ◽

Interference Test

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Low-Cost Measurement of Hydraulic Fracture Dimensions Using Pressure Data in Treatment and Observation Wells – A Workflow for Every Well

10.2118/204183-ms ◽

2021 ◽

Author(s):

A. Kirby Nicholson ◽

Robert C. Bachman ◽

R. Yvonne Scherz ◽

Robert V. Hawkes

Keyword(s):

Hydraulic Fracturing ◽

Real Time ◽

Hydraulic Fracture ◽

Full Scale ◽

Pressure Data ◽

Observation Well ◽

High Quality ◽

Fracture Length ◽

Geometry Model ◽

Observation Wells

Abstract Pressure and stage volume are the least expensive and most readily available data for diagnostic analysis of hydraulic fracturing operations. Case history data from the Midland Basin is used to demonstrate how high-quality, time-synchronized pressure measurements at a treatment and an offsetting shut-in producing well can provide the necessary input to calculate fracture geometries at both wells and estimate perforation cluster efficiency at the treatment well. No special wellbore monitoring equipment is required. In summary, the methods outlined in this paper quantifies fracture geometries as compared to the more general observations of Daneshy (2020) and Haustveit et al. (2020). Pressures collected in Diagnostic Fracture Injection Tests (DFITs), select toe-stage full-scale fracture treatments, and offset observation wells are used to demonstrate a simple workflow. The pressure data combined with Volume to First Response (Vfr) at the observation well is used to create a geometry model of fracture length, width, and height estimates at the treatment well as illustrated in Figure 1. The producing fracture length of the observation well is also determined. Pressure Transient Analysis (PTA) techniques, a Perkins-Kern-Nordgren (PKN) fracture propagation model and offset well Fracture Driven Interaction (FDI) pressures are used to quantify hydraulic fracture dimensions. The PTA-derived Farfield Fracture Extension Pressure, FFEP, concept was introduced in Nicholson et al. (2019) and is summarized in Appendix B of this paper. FFEP replaces Instantaneous Shut-In Pressure, ISIP, for use in net pressure calculations. FFEP is determined and utilized in both DFITs and full-scale fracture inter-stage fall-off data. The use of the Primary Pressure Derivative (PPD) to accurately identify FFEP simplifies and speeds up the analysis, allowing for real time treatment decisions. This new technique is called Rapid-PTA. Additionally, the plotted shape and gradient of the observation-well pressure response can identify whether FDI's are hydraulic or poroelastic before a fracture stage is completed and may be used to change stage volume on the fly. Figure 1Fracture Geometry Model with FDI Pressure Matching Case studies are presented showing the full workflow required to generate the fracture geometry model. The component inputs for the model are presented including a toe-stage DFIT, inter-stage pressure fall-off, and the FDI pressure build-up. We discuss how to optimize these hydraulic fractures in hindsight (look-back) and what might have been done in real time during the completion operations given this workflow and field-ready advanced data-handling capability. Hydraulic fracturing operations can be optimized in real time using new Rapid-PTA techniques for high quality pressure data collected on treating and observation wells. This process opens the door for more advanced geometry modeling and for rapid design changes to save costs and improve well productivity and ultimate recovery.

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Correlation and Interpretation of Microseismic Responses using Pressure Measurements in Offset Observation Wells

10.2118/spe-173386-ms ◽

2015 ◽

Author(s):

Robert Downie ◽

Joel Le Calvez ◽

Barry Dean ◽

Jeff Rutledge

Keyword(s):

Surface Pressure ◽

Source Parameters ◽

Reservoir Pressure ◽

Pressure Measurements ◽

Observation Well ◽

Fracture Pressure ◽

Microseismic Data ◽

Pressure Depletion ◽

Microseismic Events ◽

Observation Wells

Abstract Interpretation of the microseismic data acquired during hydraulic fracture treatments is based on a variety of techniques that make use of the locations, times, and source parameters of the detected events, in conjunction with the stimulation treatment data. It is sometimes possible to observe trends or changes in the microseismic data that correspond to the surface pressure measurements; however this aspect of interpretation becomes problematic due the variability of fluid friction, slurry density, perforation restrictions, and other near-wellbore pressures when computing bottom hole fracturing pressure. An interpretation technique is proposed that uses pressure measurements in observation wells that are offset to the treatment well during microseismic interpretations. The observation well can be any well with open perforations in close proximity to the treatment well. The observation well pressures are not affected by the many complicating factors that are encountered when estimating pressure in the fracture from the surface pressure measured in the treatment well. Example data from field observations are used to demonstrate that the detection of microseismic events near an observation well and corresponding detection of fluid pressure from the fracture in the observation well validates the calculated event locations. The relationship between fracture pressure, the state of stress, and microseismic responses is discussed using Mohr-Coulomb failure criteria. Observation-well pressures and microseismic events are also used to identify instances where reservoir pressure depletion near the observation well affects surface operations at the treatment well. The results of the study show that reliable measurements of fracture pressure for use in microseismic interpretations can be obtained from offset observation wells, and where reservoir pressure depletion causes deviations from expected fracture behavior. The results also show that microseismic responses are directly related to fracture pressure, and not simply the presence of fracturing fluid itself, leading to an improved understanding of the conditions under which microseismic events occur.

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Toward Controllable Infill Completions Using Frac-Driven Interactions FDI Data

10.2118/206306-ms ◽

2021 ◽

Author(s):

Yuzhe Cai ◽

Arash Dahi Taleghani

Keyword(s):

Pressure Fluctuations ◽

Pressure Response ◽

Sudden Increase ◽

Short Period ◽

Coupled Geomechanics ◽

Multi Phase ◽

Shale Oil Reservoirs ◽

Pressure Changes ◽

Observation Wells ◽

Bottomhole Pressure

Abstract Infill completions have been explored by many operators in the last few years as a strategy to increase ultimate recovery from unconventional shale oil reservoirs. The stimulation of infill wells often causes pressure increases, known as fracture-driven interactions (FDIs), in nearby wells. Studies have generally focused on the propagation of fractures from infill wells and pressure changes in treatment wells rather than observation wells. Meanwhile, studies regarding the pressure response in the observation (parent) wells are mainly limited to field observations and conjecture. In this study, we provide a partialcorrective to this gap in the research.We model the pressure fluctuations in parent wells induced by fracking infill wells and provide insight into how field operators can use the pressure data from nearby wells to identify different forms of FDI, including fracture hit (frac-hit) and fracture shadowing. First,we model the trajectory of a fracture propagating from an infill well using the extended finite element methods (XFEM). This method allows us to incorporatethe possible intersection of fractures independent of the mesh gridding. Subsequently, we calculate the pressure response from the frac-hit and stress shadowing using a coupled geomechanics and multi-phase fluid flow model. Through numerical examples, we assess different scenarios that might arise because of the interactions between new fractures and old depleted fractures based on the corresponding pressure behavior in the parent wells. Typically, a large increase in bottomhole pressure over a short period is interpreted as a potential indication of a fracture hit. However, we show that a slower increase in bottomhole pressure may also imply a fracture hit, especially if gas repressurization was performed before the infill well was fracked. Ultimately, we find that well storage may buffer the sudden increase in pressure due to the frac-hit. We conclude by summarizing the different FDIs through their pressure footprints.

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Explicit Deconvolution of Well Test Data Dominated by Wellbore Storage

Abstract and Applied Analysis ◽

10.1155/2014/912395 ◽

2014 ◽

Vol 2014 ◽

pp. 1-12

Author(s):

K. Razminia ◽

A. Hashemi ◽

A. Razminia ◽

D. Baleanu

Keyword(s):

Test Data ◽

Material Balance ◽

Early Time ◽

Time Behavior ◽

Well Test ◽

Deconvolution Method ◽

Pressure Data ◽

Practical Applications ◽

Wellbore Storage ◽

Storage Effects

This paper addresses some methods for interpretation of oil and gas well test data distorted by wellbore storage effects. Using these techniques, we can deconvolve pressure and rate data from drawdown and buildup tests dominated by wellbore storage. Some of these methods have the advantage of deconvolving the pressure data without rate measurement. The two important methods that are applied in this study are an explicit deconvolution method and a modification of material balance deconvolution method. In cases with no rate measurements, we use a blind deconvolution method to restore the pressure response free of wellbore storage effects. Our techniques detect the afterflow/unloading rate function with explicit deconvolution of the observed pressure data. The presented techniques can unveil the early time behavior of a reservoir system masked by wellbore storage effects and thus provide powerful tools to improve pressure transient test interpretation. Each method has been validated using both synthetic data and field cases and each method should be considered valid for practical applications.

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