Identifying and Evaluating Producing Horizons in Fractured Basement

Tandom, P.M.; Ngoc, Nguyen Huy; Tjia, H. D.; Lloyd, Peter M.

doi:10.2118/57324-ms

Cited by 16 publications

(7 citation statements)

References 3 publications

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“…Several new well results indicate the likelihood of this hypothesis (e.g. Tandom et al 2001;Koning 2001) with wells drilled in the hanging wall showing higher fracture density and better oil production.…”

Section: Discussionmentioning

confidence: 99%

Modelling fracture systems in extensional crystalline basement

Sanders

Fullarton

Calvert

2003

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Using observations from the extensional basin setting in Vietnam, conceptual models were developed to simulate and analyse fracture systems typical of crystalline basement in such structural settings. Information from field observations, seismic surveys and three-dimensional (3-D) structural modelling were integrated and used to build geologically realistic 3-D fracture networks. A major advantage of the method used in this study is that it allows a better understanding of the apparently chaotic fracture networks characteristic of such rocks, and of the processes responsible for fracturing. Several fracture generating processes are discussed and modelled, with emphasis on tectonic fractures and the relation to structural modelling. An example is presented highlighting the differences in fracturing in the hanging wall and footwall during lithospheric extension superimposed on a primary (igneous) cooling fracture network. Results suggest that during flexural uplift, the hanging wall is significantly more deformed than the footwall, implying the former is more prone to fracturing than the footwall for both kinematic and flexural isostatic processes.Fractured basement has proved to be a successful petroleum play in the extensional offshore setting of SW Vietnam ( Fig. 1 and Areshev et al. 1992).The unconventional nature of this play demands different exploration and production strategies compared with sedimentary plays. Typically a comprehensive exploration strategy is ill defined. Cartoon style concepts have been defined (e.g. Areshev et al. 1992;Tandom et al. 1997), but few attempts have been made to link the concepts in a quantitative way to the available data, and to test these concepts in a predictive manner.The structurally high horst blocks form the usual target (Fig. 2). The seal on the fractured reservoir is formed by shale deposits overlying the basement. The basement is most probably charged with hydrocarbons from the side and above from the earliest clastic lacustrine deposits (Sladen 1997). The presence of an extensive connected fracture network in the basement then defines whether a fault block is a potential viable prospect.In this paper we reassess some of the structural concepts that define the petroleum play. Modern methods of appraising fractured reservoirs rely on a number of data sets including those from cores, FMI, wireline, video and field observations. More often than not, the prediction of regional fracture networks requires a full understanding of these diverse data sets. Here we present a novel technique that incorporates all available data into a comprehensive model describing the range of fracture systems found in extensional settings in crystalline rocks. In the absence of primary porosity and permeability, the basement reservoir potential is entirely defined by fractures forming the secondary porosity and permeability. Fracture appraisal is therefore of prime importance for the successful development of these fields. Three basic questions arise from this, namely: (1) where are the frac...

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Section: Discussionmentioning

confidence: 99%

Modelling fracture systems in extensional crystalline basement

Sanders

Fullarton

Calvert

2003

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“…However, the correlation developed for some wells of a field may not correspond with results obtained in other wells in the same field (Kumar et al, 2002;Kumar et al, 2004). Fracture analysis and evaluation using microresistivity images and stoneley acoustic waveforms has been used in fractured basements to develop geological models and define an evaluation strategy for identifying the hydrocarbon zones (Tandom et al, 1999); however, this methodology is dependent upon extensive data availability across the entire field. The smearing effect of gas on the microresistivity image has also been cited as one of the ways to identify gas-bearing intervals in tight unconventional reservoirs (Eubanks, 2008) but has limited applicability in an oil-bearing basement environment.…”

Section: Introductionmentioning

confidence: 99%

Wireline Formation Tester Complemented by Integrated Petrophysical Evaluation Characterizes an Unconventional Reservoir: A Case Study from Western Onshore India

et al. 2012

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The focus on unconventional opportunities is growing in several basins worldwide. As unconventional opportunities grow and develop, a reliable evaluation of unconventional resources and reserves poses a challenge to our industry. The novelty of many unconventional plays implies limited historical trends. Also, because no two unconventional plays are the same and variations within a play can yield significantly different results, the evaluation of such reservoirs is a challenge.In the case study presented, a workflow is described in which trap wash overlying a fractured basement was successfully evaluated for the first time using the wireline-conveyed dual packer interval pressure transient testing (IPTT) technique. An integrated petrophysical evaluation including nuclear magnetic resonance (NMR) was used for hydrocarbon saturation and permeability determination in conjunction with classical openhole logs and other advanced logs. Borehole microimagerderived results were useful in detailed fracture characterization and optimization of the dual packer position for a successful IPTT operation that proved oil from the section above fractured basement.

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“…In addition, the porosity and permeability distribution is irregular. Various methods have been developed to determine porosity and permeability distribution for such reservoirs [e.g., Kahlil et al (1993); Sibbit (1995); Tandom et al (1999); Tamagawa et al (2002); Li et al (2004); Sung and Park (2004); and Farag et al (2009)]. …”

Section: Introductionmentioning

confidence: 99%

Predicting Effective Permeability to Oil in Sandstone and Carbonate Reservoirs From Well-Logging Data

Legrand

Kok²,

Neff

et al. 2011

SPE Reservoir Evaluation &Amp; Engineering

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The fractured basement field in Yemen described in this paper is characterized by two types of fracturing: background fractures with a very low effective permeability of less than 0.001 md and fracture corridors with an effective permeability of up to several millidarcies. Except for some dissolution porosity related to fracture corridors, no significant matrix porosity is encountered (total porosity is only 1.15%). Approximately one-half of the oil in place is contained in the fracture corridors and one-half in the background fractures.Production from this field commenced in 2007. It is currently produced by depletion. Compositional grading has been observed in the 3,120-ft oil column. Despite the fact that the oil is close to bubblepoint pressure at the top of the reservoir, a moderate increase in gas/oil ratio (GOR) has been seen.Detailed studies using material balance and discrete-fracturenetwork (DFN) models revealed that the reason for the slow increase in GOR is the low permeability of the background fractures. The low permeability leads to viscous forces being dominant over gravity forces and, hence, limited gravity segregation of gas and oil.Because of the relatively small viscosity difference between the gas and the oil in this field ( o / g = 6.5), the gas mobility is not much higher than the oil mobility at low gas saturations. Hence, oil and gas are produced effectively from the background fractures into the fracture corridors and the reservoir pressure is not depleting as fast as in reservoirs with higher viscosity difference between gas and oil. This results in a more effective solution-gasdrive recovery mechanism than that expected for a conventional reservoir.A number of reservoir-management strategies have been investigated. The results indicate that the low permeability of the fracture corridors and very low permeability of the background fractures lead to low recovery factors of 14% for gas injection. However, the efficiency of solution-gas drive is higher than in conventional reservoirs.

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Identifying and Evaluating Producing Horizons in Fractured Basement

Cited by 16 publications

References 3 publications

Modelling fracture systems in extensional crystalline basement

Modelling fracture systems in extensional crystalline basement

Wireline Formation Tester Complemented by Integrated Petrophysical Evaluation Characterizes an Unconventional Reservoir: A Case Study from Western Onshore India

Predicting Effective Permeability to Oil in Sandstone and Carbonate Reservoirs From Well-Logging Data

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