Reservoir Characterization for Naturally Fractured Reservoirs

Baker, Richard; Kuppe, F.

doi:10.2523/63286-ms

Cited by 5 publications

(2 citation statements)

References 7 publications

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“…A "Buckles plot" is a graph of porosity (Φ) versus water saturation (Sw); points of equal BVW form hyperbolic curves across the plot. Because the amount of water a formation can hold by capillary pressure increases with decreasing grain size, the bulk volume of water also increases with decreasing grain size (Baker and Kuppe, 2000). If data-points are clustered along a particular hyperbolic curve, this indicate that the bulk volume of water is constant and that the formation is close to irreducible water saturation (Sw irr ).…”

Section: Reservoir Fluidsmentioning

confidence: 99%

Reservoir Characteristics of the Albian Upper Qamchuqa Formation Carbonates, Taq Taq Oilfield, Kurdistan, Iraq

Al-Qayim¹,

Rashid²

2012

Journal of Petroleum Geology

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The Albian Upper Qamchuqa Formation in NE Iraq is part of an extensive dolomitized carbonate platform developed during the Barremian – Albian over the passive continental margin of NE Arabia. Recent drilling at the Taq Taq oilfield in Kurdistan has renewed interest in this formation as a reservoir unit. In this paper, the reservoir and petrophysical characteristics of the Upper Qamchuqa Formation at Taq Taq are described using data from wireline logs, cores and thin‐sections from four wells. At Taq Taq oilfield, the Qamchuqa Formation can be divided on the basis of lithology into two units: an upper Dolomite Unit and a lower Limestone Unit. The Dolomite Unit is 140–190 m thick and is dominated by massive dolomites and dolomitic limestones. High porosity values (up to 26%, estimated from well logs) were recorded in intervals comprising fine to medium crystalline planar‐e to planar‐s type dolomite which were frequently oil stained. Pore types include microvugs, moulds, fractures, stylolites and intercrystalline porosity. The Limestone Unit is 72–55 m thick and is composed mainly of bioturbated bioclastic limestones with minor dolomites. A wide range of carbonate facies are present and are dominated by foraminiferal wacke‐packstones and rudist packstones. Wireline log data was used to characterize the reservoir quality of the Qamchuqa Formation at Taq Taq. Four porosity units were recognized. The upper porosity units has the best reservoir quality with average porosities of 15 %, compared to the second unit (7.5%), the third unit (7%) and the fourth unit (4%). Different cut‐off values were estimated, and related petrophysical parameters were evaluated and were used to subdivide the reservoir succession into three reservoir units. The uppermost of these units was found to have the best reservoir characteristics and represents the upper part of the Dolomite Unit. It has a thickness of 31–43.5 m with 25–41 m of net pay and 82% oil saturation. Flow in this unit is dual, dominated by fracture flow superimposed on matrix flow.

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Section: Reservoir Fluidsmentioning

confidence: 99%

Reservoir Characteristics of the Albian Upper Qamchuqa Formation Carbonates, Taq Taq Oilfield, Kurdistan, Iraq

Al-Qayim¹,

Rashid²

2012

Journal of Petroleum Geology

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“…Such an approach to the characterization of NFRs combines two historically developed methods; namely 'direct' (geological) and 'inverse' (engineering) (12) . Using static data, direct methods investigate the relationships between fracture characteristics (such as length, aperture, spacing, connectivity, etc.)…”

Section: Methodsmentioning

confidence: 99%

Characterization of Fracture Network System of the Midale Field

Bogatkov

Babadagli

2009

Journal of Canadian Petroleum Technology

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Enhanced oil recovery from challenging/complex fields requires extensive analysis of reservoir structure and good understanding of the effect of this structure on the dynamics of the process. Naturally fractured reservoirs are good examples of this kind and their fracture network characterization is still a bigchallenge. In this study, we analyzed the fracture network system of a portion of the Midale Field, a naturally fractured carbonate reservoir in the Williston Basin of southeastern Saskatchewan, Canada. Our study aims at an extensive characterization of fracture and fracture network properties and construction of a reliable fracture network model for further use in assessing the oil recovery by CO2 injection and CO2 sequestration potential. We integrated static data such as cores, logs and well tests to build 3D discrete fracture network models. Stochastic numerical approach was applied using a commercial software package. A fracture network constructed from static data was calibrated using well test data. Several parameters were evaluated in sensitivity studies to determine those characteristics of the network which have higher influence on the reservoir performance. Simulated well test response was checked against previously published well test data. This study allowed us to recognize uncertainties in critical parameters and propose some measures to manage those uncertainties. Introduction The Midale is a carbonate field located in southeastern Saskatchewan. Following the discovery in 1953, the field was developed on 32 ha spacing and proved to bear 81.9 ? 106 Sm3 reserves of 28.7 °API oil. The field belongs to the Mississippian oil trend located along the northern margin of Williston Basin. Subsequent to primary production up to 1962, the field was subjected to waterflooding on 83 inverted nine-spot patterns. To maintain the production which declined after 1964, an intensive program of vertical and horizontal infill drilling was undertaken. As of the end of 2006, approximately 1,000 wells exist in the field and more than 25% of OOIP was produced with an average watercut of 92%(1). The Midale Field is currently being subjected to tertiary recovery by miscible CO2 flooding. This field-scale CO2 injection was preceded by a 1.78 ha pilot project in 1984 ? 1989 which paved the way for a larger demonstration project. The CO2 Flood Demonstration Project encompassed 10% of the Midale Unit and paved the way for the field-scale application, which is expected to end up with an incremental recovery of 15% of OOIP(2). The Midale Field does not meet typical screening criteria for CO2 flooding. Nevertheless, extensive research and field applications proved that a proper design based on the analyses of the special combination of petrophysical, lithological and fracturing data can result in a successful carbon dioxide flood. The 24 m thick Midale Reservoir section consists of two main layers: dolomite-dominated "Marly" and vugular limestone, called "Vuggy". Both strata contain systematic fractures, though the degree of fracturing varies. Numerous studies conducted on the field revealed some characteristics of the natural fracture network (NFN) by both inverse methods, such as waterflood and carbon dioxide flood performance analyses, and well test analyses and direct methods such as core and log analyses.

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

Kuchuk

Biryukov

Fitzpatrick

et al. 2015

SPE Annual Technical Conference and Exhibition

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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

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Reservoir Characterization for Naturally Fractured Reservoirs

Cited by 5 publications

References 7 publications

Reservoir Characteristics of the Albian Upper Qamchuqa Formation Carbonates, Taq Taq Oilfield, Kurdistan, Iraq

Reservoir Characteristics of the Albian Upper Qamchuqa Formation Carbonates, Taq Taq Oilfield, Kurdistan, Iraq

Characterization of Fracture Network System of the Midale Field

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

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