Formation Chlorine Measurement From Spectroscopy Enables Water Salinity Interpretation: Theory, Modeling, and Applications

2020 ◽  
Vol 61 (6) ◽  
pp. 549-569
Author(s):  
Jeffrey Miles ◽  
◽  
Laurent Mossé ◽  
Jim Grau ◽  
◽  
...  
Keyword(s):  
Water Saturation ◽  
Laboratory Data ◽  
Chloride Concentration ◽  
Chlorine Concentration ◽  
Nuclear Spectroscopy ◽  
Water Salinity ◽  
Water Volume ◽  
Simultaneous Estimation ◽  
Diverse Range ◽  
Radial Depth

Many methods of calculating water saturation require knowing the chloride concentration in formation water. Chlorides have a strong effect on water properties, and they impact saturation estimates that are based on resistivity, dielectric dispersion, or thermal neutron absorption. Here we introduce a new direct quantitative measurement of formation chlorine from nuclear spectroscopy, enabling a continuous log of water salinity within a limited radial depth. Neutron capture spectroscopy is sensitive to chlorine and is a natural fit for measuring its concentration, except that the spectrum contains chlorine from both the formation and borehole. The borehole chlorine background can be large and is highly variable. Historical efforts to derive water salinity from spectroscopy have relied on ratios of chlorine and hydrogen, which are affected by the borehole and hydrocarbons. The direct use of chlorine provides a more reliable basis for salinity interpretation after isolating its formation signal. We partition the borehole and formation components of chlorine via two unique spectral standards. The contrast between the two standards arises from differences in gamma ray scattering based on their point of origin. The shape of the borehole chlorine standard must be adjusted along depth to account for environmentally dependent scattering, which we achieve with a continuously varying function of borehole and formation properties. The algorithm is derived from 129 laboratory measurements and 2,995 numerical simulations spanning a diverse range of conditions. The remaining signal is converted into a log of formation chlorine concentration. In combination with total porosity, chlorine concentration sets a minimum value for water salinity. Adding an organic carbon measurement enables the simultaneous estimation of water volume and salinity. Chlorine concentration can also be combined with a selected water salinity to compute a water volume for comparison with other methods. Finally, chlorine concentration enables calculation of a maximum expected sigma, which can identify the presence of excess thermal absorbers in the matrix. The systematic uncertainty on the chlorine concentration ranges from 0.03 to 0.07 wt%, depending on borehole size. The resulting salinity accuracy is inversely proportional to porosity. A potential limitation of the measurement is its depth of investigation, reaching 8 to 10 in. for 90% of the signal. The chlorine concentration is sensitive to filtrate or connate water, depending on formation permeability and invading fluids. We first present the technique to measure formation chlorine, supported by modeling, laboratory data, and core-log comparisons. We then propose petrophysical workflows to interpret the chlorine concentration.

REVISING THE INTERPRETATION OF COMPLEX CARBONATE RESERVOIRS WITH THE USE OF NOVEL ADVANCED LOGS INTEGRATION TECHNIQUES

2021 ◽  
Author(s):  
Harish B. Datir ◽  
◽  
Laurent Mosse ◽  
Terje Kollien ◽  
◽  
...  
Keyword(s):  
Barents Sea ◽  
Water Saturation ◽  
Variable Parameter ◽  
Dielectric Dispersion ◽  
Volume Estimation ◽  
Nuclear Spectroscopy ◽  
Water Salinity ◽  
Present Contribution ◽  
Integration Techniques ◽  
Formation Water Salinity

The Alta field in the Barents Sea was discovered in 2014. The reservoir formation is primarily carbonate rocks with high formation water salinity. Extensive waterflooding processes have led to an approximately 200-m rise of water level. The complexities anduncertainties regarding imbibition, current free waterlevel, and pseudo fluid contacts within the field translateinto uncertainty in the hydrocarbon volume estimation. Initial, triple-combo-based petrophysical evaluations have already been updated using advanced log measurements, as reported in an earlier publication. The evaluation is now consolidated by using two new techniques relying on advanced spectroscopy logging and combination with dielectric dispersion logging. Their objective is to further reduce the uncertainty in water saturation associated with variable apparent water salinity. The present contribution proposes a workflow that relies on two novel techniques. The first technique is a direct quantitative measurement of formation chlorine concentration from nuclear spectroscopy, which helps resolve the formation's apparent water salinity and provides a way to calibrate formation matrix sigma. The second technique relies on the existing combined inversion of dielectric dispersion and formation sigma, including explicitly invasion effects. This second technique benefits from the first technique's insight to adjust sigma interpretation and provide bounds for possible salinity variations. The workflow provides robust flushed and unflushed zone salinities, here the most uncertain and variable parameter, combined with accurate estimations of virgin and residual hydrocarbon saturations. The quantification of dielectric textural parameters describing how the water is shaped inside the formation is also improved, contributing to the improvement of virgin zone hydrocarbon saturation estimation.

UNCERTAINTY QUANTIFICATION BY MONTE CARLO SIMULATION OF LAB-DERIVED SATURATION DATA FROM SPONGE CORES

2021 ◽  
Author(s):  
Mohammed Alghazal ◽  
◽  
Dimitrios Krinis ◽  
Keyword(s):  
Monte Carlo Simulation ◽  
Monte Carlo ◽  
Material Balance ◽  
Water Salinity ◽  
Water Evaporation ◽  
Water Volume ◽  
Distilled Water ◽  
Core Data ◽  
Fluid Saturation ◽  
Core Saturation

Fluid saturation data obtained from core analysis are used as control points for log calibration, saturation modeling and sweep evaluation. These lab-derived data are often viewed as ground-truth values without fundamentally understanding the key limitations of experimental procedures or scrutinizing the accuracy of measured lab data. This paper presents a unique assessment of sponge core data through parameterization, uncertainty analysis and Monte-Carlo modeling of critical variables influencing lab-derived saturation results. This work examines typical lab data and reservoir information that could impact final saturation results in sponge coring. We dissected and analyzed ranges of standard raw data from Dean-Stark and spectrometric analysis (including, gravimetric weights, distilled water volumes, pore volumes and sponge’s absorbance), input variables of fluid and rock properties (such as, water salinity, formation volume factors, plug’s dimension and stress corrections), governing equations (including, salt correction factors, water density correlations and lab mass balance equations) and other factors (for instance, sources of water salinity, filtrate invasion, bleeding by gas liberation and water evaporation). Based on our investigation, we have identified and statistically parameterized 11 key variables to quantify the uncertainty in lab-derived fluid saturation data in sponge cores. The variables’ uncertainties were mapped into continuous distributions and randomly sampled by Monte-Carlo simulation to generate probabilistic saturation models for sponge cores. Simulation results indicate the significance of the water salinity parameter in mixed salinity environments, ranging between 20,000 to 150,000 ppm. This varied range of water salinity produces a wide uncertainty spectrum of core oil saturation in the range of +/- 3 to 10% saturation unit. Consequently, we developed two unique salinity variance models to capture the water salinity effect and minimize the uncertainty in the calculation of core saturation. The first model uses a material balance to solve for the salinity given the distilled water volume and gravimetric weight difference of the sample before and after leaching. The second model iteratively estimates the salinity required to achieve 100% of total fluids saturation at reservoir condition after correcting for the bleeding, stress and water evaporation effects. Our work shows that these derived models of water salinity are consistent with water salinity data from surface and bottom-hole samples. Despite the prominence of applications of core saturation data in many aspects of the industry, thorough investigation into its quality and accuracy is usually overlooked. To the best of our knowledge, this is the first paper to present a novel analysis of the uncertainty coupled with Monte-Carlo simulation of lab-derived saturation’s data from sponge cores. The modeling approach and results highlighted in this work provide the fundamental framework for modern uncertainty assessment of core data.

scholarly journals K-Mean Cluster Analysis for Better Determining the Sweet Spot Intervals of the Unconventional Organic-Rich Shale: A Case Study

2018 ◽  
Vol 7 (2) ◽  
pp. 200-213
Author(s):  
Muhammad Nur Ali Akbar ◽  
Septian Tri Nugraha
Keyword(s):  
Organic Matter ◽  
Water Saturation ◽  
Laboratory Data ◽  
Organic Content ◽  
Brittleness Index ◽  
Sweet Spot ◽  
Typing Method ◽  
Log Data ◽  
Gas Saturation

Abstract The petrophysical analysis is the crucial task for evaluating the quality of unconventional organic-rich shale and tight gas reservoirs. The presence of organic matter and the ultra-tight with over complex pore system have remained a lack of understanding of how to evaluate the extensive parameters of porosity considering organic content, gas saturation, organic richness, brittleness index, and sweet spot interval by only using conventional log. Therefore, this study offers effectively applied techniques and better analysis for interpreting these parameters by maximizing and integrating geological, geochemical, rock mechanical and engineering data. In general, the field data used in this study are from the first dedicated well for source rock exploration in the North Sumatra Basin, Indonesia. The developed method was derived by using conventional log. All interpretation results were validated by laboratory data measurements of routine and special core analysis, petrography, total organic carbon (TOC) and organic maturation, and brittleness index (BI) calculation. Moreover, the high quality of NMR log data was used as well to ensure our developed techniques present good estimations. Briefly about the methods, we started to determine the total and effective porosity based on the density log by including the presence of organic matter and multi-mineral analysis in these estimations. Then, we used the revised water saturation-TOC of water saturation while the TOC was predicted in advance by averaging three results from the correlation of TOC-Density, modified CARBOLOG and Passey’s ΔlogR methods. Equally important, in order to obtain the reliable gas saturation prediction, we used saturation exponent (n), cementation factor (m), and the tortuosity factor (a) parameters which obtained from laboratory measurement of formation resistivity factor and resistivity index (FFRI). In addition, the brittleness index was predicted based on sonic log data. Finally, all parameters needed for determining gas shale sweet spot have been made. Then, we developed a way to evaluate the sweet spot interval by using K-mean clustering. In conclusion, this clustering result properly follows the shale quality index parameters which consist of organic richness and maturation, brittleness index, the storage capacity of porosity and gas saturation. This study shows that these petrophysical applied techniques leads us to interpret the best position of shale interval to be developed with a simple, fast, and accurate prediction way. Furthermore, as a novelty, this method can be used as rock typing method and obviously can reduce uncertainty and risks in organic-rich shale exploration.

Defining irreducible water saturation using global characteristics envelopes and novel correlations

2016 ◽  
Vol 56 (1) ◽  
pp. 1 ◽  
Author(s):  
Peter Behrenbruch ◽  
Chengzhi Yuan ◽  
Nhan B. Truong ◽  
Phil Do Huu ◽  
Tuan G. Hoang
Keyword(s):  
Grain Size ◽  
Pore Structure ◽  
Water Saturation ◽  
Laboratory Data ◽  
Great Promise ◽  
Flow Zone ◽  
Structure Characteristics ◽  
Irreducible Water Saturation ◽  
Universal Correlation ◽  
Group Flow

Irreducible water saturation plays a significant role in estimating hydrocarbon initially-in-place and petroleum recovery. Yet, laboratory measurements for determining irreducible water saturation take considerable time and money. For this reason available data may not cover all requirements, giving rise to the practise of using correlations to fill in gaps. Described in this paper are the reasons for irreducible water saturation being an elusive parameter that not only depends on pore structure characteristics but also the type of experiment and laboratory procedures, as well as changing plug conditions during experimentation. This paper reviews traditional methods, as well as recent and novel approaches to quality assure laboratory data and for correlating irreducible water saturation for prediction. To gain insight into the dependence of irreducible water saturation on detailed pore structure characteristics, most notably grain size and sorting, the usefulness of global characteristics envelopes is explored (Behrenbruch and Biniwale, 2005). In this multidimensional plot, irreducible water saturation is plotted against porosity, permeability, hydraulic radius, porosity group, flow zone indicator (grain size) and sorting, giving an insightful overview of the interdependence of parameters. The second part of this paper compares novel correlations with commonly used correlations. Traditional and more recent correlations are covered, from simple correlations versus the logarithm of permeability to more sophisticated approaches using more variables, including porosity and others. Most notably, it is shown that an approach of correlating irreducible water saturation with grain size (or flow zone indicator [FZI]) and sorting shows great promise. Data from two Australian fields are used to demonstrate the methodology, showing a significant increase in fitting accuracy. This approach may eventually lead to a universal correlation.

scholarly journals Insights, Trends and Challenges Associated with Measuring Coal Relative Permeability

2019 ◽  
Vol 89 ◽  
pp. 01004
Author(s):  
Dylan Shaw ◽  
Peyman Mostaghimi ◽  
Furqan Hussain ◽  
Ryan T. Armstrong
Keyword(s):  
Relative Permeability ◽  
Effective Stress ◽  
History Matching ◽  
Water Saturation ◽  
Laboratory Data ◽  
Stress Regime ◽  
Cross Point ◽  
Irreducible Water Saturation ◽  
Relative Permeability Curves ◽  
The Right

Due to the poroelasticity of coal, both porosity and permeability change over the life of the field as pore pressure decreases and effective stress increases. The relative permeability also changes as the effective stress regime shifts from one state to another. This paper examines coal relative permeability trends for changes in effective stress. The unsteady-state technique was used to determine experimental relativepermeability curves, which were then corrected for capillary-end effect through history matching. A modified Brooks-Corey correlation was sufficient for generating relative permeability curves and was successfully used to history match the laboratory data. Analysis of the corrected curves indicate that as effective stress increases, gas relative permeability increases, irreducible water saturation increases and the relative permeability cross-point shifts to the right.

Incorporating mechanisms of fluid pressure relaxation into inclusion‐based models of elastic wave velocities

Geophysics ◽  
2003 ◽  
Vol 68 (4) ◽  
pp. 1173-1181 ◽  
Author(s):  
S. Richard Taylor ◽  
Rosemary J. Knight
Keyword(s):  
Elastic Wave ◽  
Water Saturation ◽  
Laboratory Data ◽  
Fluid Pressure ◽  
P Wave ◽  
Porous Rocks ◽  
Low Frequencies ◽  
Wave Velocities ◽  
Exact Agreement ◽  
Flow Through

Our new method incorporates fluid pressure communication into inclusion‐based models of elastic wave velocities in porous rocks by defining effective elastic moduli for fluid‐filled inclusions. We illustrate this approach with two models: (1) flow between nearest‐neighbor pairs of inclusions and (2) flow through a network of inclusions that communicates fluid pressure throughout a rock sample. In both models, we assume that pore pressure gradients induce laminar flow through narrow ducts, and we give expressions for the effective bulk moduli of inclusions. We compute P‐wave velocities and attenuation in a model sandstone and illustrate that the dependence on frequency and water‐saturation agrees qualitatively with laboratory data. We consider levels of water saturation from 0 to 100% and all wavelengths much larger than the scale of material heterogeneity, obtaining near‐exact agreement with Gassmann theory at low frequencies and exact agreement with inclusion‐based models at high frequencies.

Water saturation and permeability from resistivity, dielectric, and porosity logs

Geophysics ◽  
1995 ◽  
Vol 60 (6) ◽  
pp. 1756-1764 ◽  
Author(s):  
Olivar A. L. de Lima
Keyword(s):  
Volume Fraction ◽  
Water Saturation ◽  
Laboratory Data ◽  
Type Equation ◽  
Oil Well ◽  
Exchange Cation ◽  
Potiguar Basin ◽  
Porosity Logs ◽  
New Equation ◽  
Type Parameter

An analytical approach previously proposed to model the electrical properties of shaly sands has been adapted to obtain the cementation exponent (m), the water saturation [Formula: see text], and the shaliness distribution from electromagnetic and porosity log measurements in an oil well. Shaliness is described by the clay volume fraction (p) and by the clay type parameter [Formula: see text] in the sand. For a shale‐coating structure these parameters can be related to the exchange cation density [Formula: see text]. Based on an equivalent flow regime inside this granular model, a Kozeny‐Carman type equation has been derived, expressing the intrinsic permeability (k) of the medium in terms of a porosity‐tortuosity factor [Formula: see text] and of the parameter [Formula: see text]. The power‐law derived expression shows that k decreases with the amount of clay, not only because a high [Formula: see text] implies a narrowing of the pore channels, but also because it modifies the hydraulic tortuosity of the medium. This new equation has been statistically tested with extensive petrophysical laboratory data for different types of sandstones and satisfactorily applied to core and log data of an oil well from Potiguar Basin, Rio Grande do Norte, Brazil.

Formation Evaluation With NMR, Resistivity, and Pressure Data: A Case Study of a Carbonate Oil Field Off shore West Africa

2021 ◽  
Vol 62 (1) ◽  
pp. 73-88
Author(s):  
Ting Li ◽  
◽  
Nicholas Drinkwater ◽  
Karen Whittlesey ◽  
Patrick Condon ◽  
...  
Keyword(s):  
West Africa ◽  
Water Saturation ◽  
Pore Space ◽  
Free Water ◽  
Total Porosity ◽  
Poor Quality ◽  
Oil Field ◽  
Water Volume ◽  
Pressure Gradients ◽  
Irreducible Water Saturation

In this paper, we examine fluids interpretation techniques in a prolific oil field in offshore West Africa. A sourceless logging program, consisting of logging-while-drilling (LWD) nuclear magnetic resonance (NMR), resistivity, and formation tester, was chosen to log the reservoir section in 6.5-in. holes. The purpose of this study is to answer questions related to asset appraisal and development with these limited measurements. Core data available are porosity, permeability, water salinity, Archie m and n, and Dean-Stark Sw. A comparison of the core and NMR log indicates that NMR total porosity is not affected by hydrocarbon in the pore space. We use a statistical method called factor analysis to deconvolve independent fluid modes from the T2 distribution and pick the T2 cutoff. The NMR irreducible water saturation (Swirr) computed with this cutoff agrees with Dean-Stark Sw. Continuous Sw is calculated with Archie’s equation with lab-measured parameters and validated against Dean-Stark Sw above the transition zone. The Timur-Coates model is used to estimate matrix permeability. The first application of this interpretation workflow is to confirm the free-water level (FWL) derived from pressure gradients. We found the Sw profile largely controlled by heterogeneity in rock textures. The presence of both good and poor-quality rocks makes log-based FWL picking difficult. We use Swirr from NMR to indicate rock quality and simplify our final interpretation. The FWL found by sourceless log interpretation is consistent with the initial FWL found by pressure gradients. The second application is perforation design. Zones with good porosity and low mobile water volume are selected for perforation, and a safe distance is maintained from FWL. As a result, all producer wells exhibit zero water cut.

scholarly journals Chloride Transport in Undersea Concrete Tunnel

2016 ◽  
Vol 2016 ◽  
pp. 1-10 ◽  
Author(s):  
Yuanzhu Zhang ◽  
Xiaozhen Li ◽  
Guohua Yu
Keyword(s):  
Water Saturation ◽  
Chloride Transport ◽  
Water Pressure ◽  
Chloride Concentration ◽  
Solution Concentration ◽  
Chloride Diffusion ◽  
Hydraulic Pressure ◽  
Chloride Diffusion Coefficient ◽  
External Water Pressure ◽  
External Water

Based on water penetration in unsaturated concrete of underwater tunnel, a diffusion-advection theoretical model of chloride in undersea concrete tunnel was proposed. The basic parameters including porosity, saturated hydraulic conductivity, chloride diffusion coefficient, initial water saturation, and moisture retention function of concrete specimens with two water-binder ratios were determined through lab-scale experiments. The variation of chloride concentration with pressuring time, location, solution concentration, initial saturation, hydraulic pressure, and water-binder ratio was investigated through chloride transport tests under external water pressure. In addition, the change and distribution of chloride concentration of isothermal horizontal flow were numerically analyzed using TOUGH2 software. The results show that chloride transport in unsaturated concrete under external water pressure is a combined effect of diffusion and advection instead of diffusion. Chloride concentration increased with increasing solution concentration for diffusion and increased with an increase in water pressure and a decrease in initial saturation for advection. The dominant driving force converted with time and saturation. When predicting the service life of undersea concrete tunnel, it is suggested that advection is taken into consideration; otherwise the durability tends to be unsafe.

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