Petrophysical Evaluation of Deep Sandstone Gas-Bearing Reservoirs Using LWD Time-Independent Logs Paradigm

Fakolujo, Kehinde M; Al-Belowi, Ali Rashed; Gzara, Kais; Onuigbo, Oluchukwu Lsd

doi:10.2118/171491-ms

Cited by 3 publications

(1 citation statement)

References 52 publications

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“…This workflow has been extended further to include non-consonant measurements (Al- Daghar et al 2015) and provide a number of other useful quantities, including, but not limited to, invasion-independent variates or hybrid measurements and moveable fluid types and volumes, as described in (Kraishan et al 2014;Fakolujo et al 2014aFakolujo et al , 2014b.…”

Section: Time-lapse Acquisition and Analysis Of Lwd Datamentioning

confidence: 99%

Maximizing Information through Data Driven Analytics in Petrophysical Evaluation of Well Logs

Jain

Gzara

Makarychev

et al. 2015

Day 3 Wed, September 30, 2015

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Modern logging data are characterized by abundance and multiple dimensions: spatial, temporal, and physical. Traditional interpretation workflows for logging data are often limited in their scope and flexibility and use only a subset of the data dimensions, either by choice or necessity. Furthermore, the various deterministic or stochastic workflows typically rely on preconceived rock and fluid models. When those a priori models do not fit the data, confusion can ensue, whereas it is obvious that the correct model is buried somewhere in the "big logging data."To overcome these limitations, new symbiotic approaches using domain expertise and data analytics ("domain-analytics") have been developed. Domain experts use those novel approaches to develop data-driven workflows to explore and mine complex logging datasets for latent but interpretable information. Once validated to be idempotent, the expert workflows that respect both the acquired data and domain knowledge can be packaged into new classes of answers products.In this paper, the novel approaches, along with the examples of new answer products, are presented. These include 1) the automated spatial search for common modes and repeated patterns in the single or multi-well nuclear magnetic resonance (NMR) data, 2) the generation of a data-driven fluid model using time-lapse logging data acquired during multiple passes over the same formation, and 3) the creation of interpretive class-based models using definitive core data that could be propagated to continuous log data for a richer petrophysical interpretation. Big Logging DataRock formations are discontinuous, heterogeneous, anisotropic media resulting from a long and often complex geological history. To understand and quantify the underlying rock matrix and fluid distribution, petrophysicists derive various quantities of interest (Q) such as lithology, pore-size distribution, fluid characteristics, and volumetrics from a number of log measurements (M), as shown in Fig. 1. Those log measurements (M) are the direct transform (g) of acquired physical data (A), whereas the transforms (h) of subsurface quantities from log measurements are mostly empirical and/or model based.Transforms between log measurements and petrophysical quantities are not only difficult to establish but are also limited in scope. Difficulty lies in the fact that most of these relationships are empirical, created by fitting observed results and measured properties in laboratories using cores and fluid samples.

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Section: Time-lapse Acquisition and Analysis Of Lwd Datamentioning

confidence: 99%

Maximizing Information through Data Driven Analytics in Petrophysical Evaluation of Well Logs

Jain

Gzara

Makarychev

et al. 2015

Day 3 Wed, September 30, 2015

Self Cite

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Formation Evaluation in Gas-Bearing Reservoirs Drilled with Na/K Formate WBM, Using LWD Time-Lapse Data Acquisition

Fakolujo

Al-Belowi

Gzara

et al. 2014

Day 3 Wed, November 12, 2014

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The introduction of formate-based drilling muds successfully addressed drilling challenges related to barite-weighted muds. The muds exhibited peculiar petrophysical properties that adversely affected log interpretation. First, the mud present inside the borehole and surrounding the tool required different environmental corrections; secondly invading mud-filtrate present inside the formation was difficult to account for. Because of the higher density, lower hydrogen index, and high gamma-ray readings associated with Na/K formate-based drilling fluids, for example, petrophysical analysis typically resulted in inaccurate mineralogy and pessimistic porosity and permeability estimates. Such estimates were also strongly dependent on the extent of invasion by the mud. Two new approaches were developed to address these long-standing challenges in gas-bearing siliciclastic and carbonate sequences. Logging-while-drilling (LWD) time-lapse data acquisition makes it possible to track changes in log measurements between a first (drill) pass and a second (wipe) pass as mud filtrate invades the formation. In a first approach, these changes reflect the contrast in petrophysical properties between the mud filtrate and the displaced native formation fluids, and can be used to estimate the unknown petrophysical properties of such mud filtrate. In a second, geometric approach, the different measurements are considered to represent different axes in measurement space, and then the axes are rotated to reduce the number of rotated measurements affected by invasion to just one. This measurement is then discarded, and the remaining rotated measurements are used. In all, up to six different petrophysical models from two different wells were compared. The results indicate a step change in petrophysical analysis in case of Na/K formate-based drilling fluids. They demonstrate how it is possible to build a robust but remarkably simple petrophysical model using only rotated nuclear measurements, with all of the following characteristics. The model is extremely stable as compared to more complex models. It requires neither knowledge of the Na/K formate mud-filtrate characteristics, nor knowledge of its volume. It does not require resistivity input, but consistently reproduces similar saturations when compared with models using resistivity as input. Data from the drill- and the wipe-pass produced identical results, independent of formation invasion.

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Invasion Corrected Fluid Saturations, from Standalone Consonant Nuclear Measurements, Using Canonical-Correlation Analysis (CCA) of Logging-While-Drilling (LWD) Time-Lapse Data

et al. 2015

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Fluids saturations in new wells are usually derived from resistivity measurements, using locally selected or calibrated resistivity equations. Some drawbacks to resistivity measurements are multiple environmental corrections in high-angle wells, thin beds, washed-out boreholes, and complex invasion profiles. Moreover, the accuracy of Archie's equation may suffer from variable cementation and saturation exponents and unknown water salinity.A recently introduced comprehensive suite of consonant logging-while-drilling (LWD) nuclear measurements with linear mixing laws, is used to solve for minerals and fluid volumes independent of resistivity measurements. This requires the petrophysical properties of all the fluids present to be known. Another requirement for accurate formation evaluation is the mud filtrate invasion correction. While this poses no problem for multiple depths of investigation (MDOI) resistivity measurements that also read deep into the formation, there is no set rule to determine the geometrical factor of nuclear measurements to account for invasion. This paper describes an LWD time-lapse data acquisition scheme to circumvent invasion effects on nuclear measurments and to eliminate the need to specify some of the unknown petrophysical properties of the fluids present. Canonical-correlation analysis (CCA) is used to identify canonical variates that remain unchanged between a primary drill pass and a secondary wipe pass. Because these variates remain unchanged between passes, they are independent of the formation invasion status, and can represent the properties of either the virgin or the flushed zone, but not a combination of the two, as is typically the case of measurements whose volume of investigation samples both zones. These invasion-independent variates are then used in the petrophysical evaluation, instead of the standard logs which may otherwise vary with time.We used CCA in 2 carbonate examples to show how to 1) correct bulk density measurement in corkscrew borehole, 2) correct MDOI capture sigma measurements for invasion effect, and 3) perform volumetric formation evaluation without knowledge of the water and hydrocarbon endpoints and invasion parameters. The CCA approach is a significant new development in well log interpretation that removes uncertainties associated with unknown mineral or fluids petrophysical properties and invasion status.

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Petrophysical Evaluation of Deep Sandstone Gas-Bearing Reservoirs Using LWD Time-Independent Logs Paradigm

Cited by 3 publications

References 52 publications

Maximizing Information through Data Driven Analytics in Petrophysical Evaluation of Well Logs

Maximizing Information through Data Driven Analytics in Petrophysical Evaluation of Well Logs

Formation Evaluation in Gas-Bearing Reservoirs Drilled with Na/K Formate WBM, Using LWD Time-Lapse Data Acquisition

Invasion Corrected Fluid Saturations, from Standalone Consonant Nuclear Measurements, Using Canonical-Correlation Analysis (CCA) of Logging-While-Drilling (LWD) Time-Lapse Data

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