Identification of Bypassed Pays in Low-Resistivity, Thinly-Bedded, Sand-Shale Sequences in the Ghdames Basin of North Africa Through Use of the Wireline Formation Tester

Chu, Wei-Chun; Welch, Paul M.

doi:10.2118/114478-ms

Cited by 8 publications

(1 citation statement)

References 7 publications

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“…Filtrate monitoring is best suited when trying to recover a lab quality PVT sample, because it typically requires a very long pumping time to produce a "clean" fluid and was not found to be cost effective here. Using both the optical density (OD) track and the GOR measurement was found to be both accurate and more cost effective in this sequence (Chu and Welch, 2008). The GOR measurement was found to be relatively smooth and repeatable in oil-bearing sections.…”

Section: Wftmentioning

confidence: 92%

A Practical Approach to Determine Low-Resistivity Pay in Clastic Reservoirs

Chu

Steckhan

2011

SPE Annual Technical Conference and Exhibition

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Low-resistivity pay (LRP) has been a challenging problem in formation evaluation for many years. This is because conventional petrophysical interpretations are unable to identify pay intervals in low-resistivity reservoirs. This paper lays out a robust workflow for identifying LRP in thinly laminated sands with silty and/or shaly layers.The workflow is essentially a two-step process which integrates data from gas while drilling (GWD), conventional logs and nuclear magnetic resonance (NMR) logs which identify potential pay intervals for further examination using wireline formation tester (WFT). This approach allows one not only to identify pay intervals but also their phase and their flow characteristics without the need of a conventional drill-stem-test (DST).It is common for LRP to have high water saturation (60-70%) computed by conventional petrophysical interpretation while producing sustained water-free oil for few years. A petrophysical study was undertaken to integrate core data analyses including conventional, NMR and mercury injection capillary pressure (MICP). Data from over 100 sidewall cores (SWC) were examined. This novel approach for estimating irreducible water saturation (S wi ) was developed based on 1. A good relationship was recognized between S wi from capillary pressure data as compared to that estimated from NMR de-saturated core. 2. A correlation was established between S wi of de-saturated core and T 2, LM . 3. A validation was performed for zones producing water-free oil to link between NMR-MICP core analysis and NMR logs, using the following two methods for estimating S wi from a. capillary pressure data that is computed with knowledge of the height above free water level (FWL), b. T 2, LM of NMR logs using the correlation developed in Step 2. The benefits of this methodology are that it improves decision in well completion, predicts well performance accurately and reduces uncertainty in reserve estimation. In addition, it allows the user not only to identify zones of pay that would have been missed using conventional analysis, but also to estimate FWL elevations with higher accuracy from a saturation height model (SHM). Saturation profiles derived by this approach and those ones modeled from saturation height equations based on MICP capillary pressure data can be fitted better due to substantial reduction in uncertainties of log derived saturation data. Consequently the initialization of in-place volumes for hydrocarbons will be enhanced.

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Section: Wftmentioning

confidence: 92%

A Practical Approach to Determine Low-Resistivity Pay in Clastic Reservoirs

Chu

Steckhan

2011

SPE Annual Technical Conference and Exhibition

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A road map for the identification and recovery of by-passed pay

Worthington¹

2010

PGC

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By-passed pay can occur at or between wells. Either way, it constitutes a lower risk prospect than hydrocarbon accumulations in unappraised areas. Beyond this, there are three contemporary drivers for its exploitation. First, new technology in the form of sharper reservoir imaging allows insights that were not achievable previously. Second, an evolving understanding of how reservoirs work has led to improved procedures for maximizing the exploitation of even the most problematic accumulations. Third, market forces amid global post-peak production fears are giving the incremental development of by-passed pay an even greater commercial impetus today. An examination of case histories that illustrate the role of these drivers has led to a six-fold type classification of by-passed pay. Type 1 can be produced using an existing identified well. Type 2 requires a side track or a new well in order to capture the reserves. Each type is further subdivided into three classes. The classification scheme has provided the context for an emerging modus operandi to maximize commercially recoverable hydrocarbons in developed assets. Thus, the approach takes the form of a road map for practical application. By corollary, the type classification demonstrably accommodates a wide range of reported exploitations of by-passed pay from diverse reservoirs. Therefore, this classification constitutes a potential foundation for further systemic refinements to the identification and recovery of by-passed pay.

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Definitive Petrophysical Evaluation of Thin Hydrocarbon Reservoir Sequences

Majid¹,

Worthington²

2012

SPE Reservoir Evaluation &Amp; Engineering

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SummaryThe petrophysical evaluation of thinly-bedded sand/shale sequences is strongly dependent on the way in which layered and dispersed shales are taken into account. There are two underpinning issues: the recognition of thin bed geometries and the estimation of shale content from lithology logs. The first of these is managed through a scenario approach, whereby different downhole scenarios are set out according to specified ranges of bed thickness. Each range has its own interpretation protocol. The second issue relates to the inherent overestimation of clay-mineral volume fraction by shale indicators and its impact on the petrophysical evaluation of thinly-bedded sand porosity. This shortcoming is managed by applying a validated scaling factor to log-derived estimates of shale volume fraction so that these become workable estimates of clay-mineral fraction for the porosity evaluation of sand layers. Both these problems become more acute for thinner beds. These two key issues are addressed conjunctively through interpretive workflows, each of which relates to a discrete range of bed thickness and uses fit-for-purpose petrophysical data sets. In particular, the multicomponent induction log is adopted as a pivotal technology for the evaluation of sand resistivity within thinly-bedded sand/shale sequences. The objective is to achieve a sound petrophysical interpretation for each downhole situation. Therefore, groundtruthing through core data is advocated where this allows the shale problem to be managed better. The outcome is a systematic approach to thin-bed evaluation, based on prescribed data inputs that optimize project effectiveness. The benefits are illustrated through case histories that demonstrate a securable upside in projected hydrocarbon volumes.

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Identification of Bypassed Pays in Low-Resistivity, Thinly-Bedded, Sand-Shale Sequences in the Ghdames Basin of North Africa Through Use of the Wireline Formation Tester

Cited by 8 publications

References 7 publications

A Practical Approach to Determine Low-Resistivity Pay in Clastic Reservoirs

A Practical Approach to Determine Low-Resistivity Pay in Clastic Reservoirs

A road map for the identification and recovery of by-passed pay

Definitive Petrophysical Evaluation of Thin Hydrocarbon Reservoir Sequences

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