Calculation of Irreducible Water Saturation (S wirr) from NMR Logs in Tight Gas Sands

2011 ◽  
Vol 42 (1) ◽  
pp. 113-125 ◽  
Author(s):  
Liang Xiao ◽  
Zhi-Qiang Mao ◽  
Yan Jin
Keyword(s):  
Water Saturation ◽  
Tight Gas ◽  
Tight Gas Sands ◽  
Irreducible Water Saturation

AN INTEGRATED PETROPHYSICAL CHARACTERIZATION OF A SILICICLASTIC TIGHT GAS RESERVOIRS IN NEUQUÉN BASIN, WESTERN ARGENTINA

2021 ◽  
Author(s):  
Nicolas Carrizo ◽  
◽  
Emiliano Santiago ◽  
Pablo Saldungaray ◽  
◽  
...  
Keyword(s):  
Water Saturation ◽  
Seismic Inversion ◽  
Tight Gas ◽  
Analysis Model ◽  
Drilling Rig ◽  
Irreducible Water Saturation ◽  
Neuquen Basin ◽  
Open Hole ◽  
Neuquén Basin ◽  
Pulsed Neutron

The Río Neuquén field is located thirteen miles north west of Neuquén city, between Neuquén and Río Negro provinces, Argentina. Historically it has been a conventional oil producer, but some years ago it was converted to a tight gas producer targeting deeper reservoirs. The targeted geological formations are Lajas, which is already a known tight gas producer in the Neuquén basin, and the less known overlaying Punta Rosada formation, which is the main objective of the current work. Punta Rosada presents a diverse lithology, including shaly intervals separating multiple stacked reservoirs that grade from fine-grained sandstones to conglomerates. The reservoir pressure can change from the normal hydrostatic gradient to up to 50% of overpressure, there is little evidence of movable water. The key well in this study has a comprehensive set of open hole logs, including NMR and pulsed-neutron spectroscopy data, and it is supported by a full core study over a 597ft section in Punta Rosada. Additionally, data from several offset wells were used, containing sidewall cores and complete sets of electrical logs. This allowed to develop rock-calibrated mineral models, adjusting the clay volume with X-ray diffraction data, porosity and permeability with confined core measurements, and link the logs interpretation to dominant pore throat radius models from MICP Purcell tests at 60,000 psi. Several water saturation models were tested attempting to adjust the irreducible water saturation with NMR and Purcell tests at reservoir conditions. As a result, three hydraulic units were defined and characterized, identifying a strong correlation with lithofacies observed in cores and image logs. A cluster analysis model allowed the propagation of the facies to the rest of the wells (50). Finally, lithofacies were distributed in a full-field 3D model, guided by an elastic seismic inversion. In the main key well, in addition to the open hole logs and core data, a cased hole pulsed neutron log (PNL) was also acquired , which was used to develop algorithms to generate synthetic pseudo open hole logs such as bulk density and resistivity, integrated with the spectroscopy mineralogical information and other PNL data to perform the petrophysical evaluation. This enables the option to evaluate wells in contingency situations where open hole logs are not possible or are too risky, and also in planned situations to replace the open hole data in infill wells, saving considerable drilling rig time to reduce costs during this field development phase. Additionally, the calibrated cased hole model can be used in old wells already drilled and cased in the Punta Rosada formation. This paper explores the integration of different core and log measurements and explains the development of rock-calibrated petrophysical and rock types models for open and cased hole logs addressing the characterization challenges found in tight gas sand reservoirs. The results of this study will be crucial to optimize the development of a new producing horizon in a mature field.

scholarly journals A new model for predicting irreducible water saturation in tight gas reservoirs

2020 ◽  
Vol 17 (4) ◽  
pp. 1087-1100
Author(s):  
Yu-Liang Su ◽  
Jin-Gang Fu ◽  
Lei Li ◽  
Wen-Dong Wang ◽  
Atif Zafar ◽  
...  
Keyword(s):  
Water Saturation ◽  
Tight Gas ◽  
Gas Reservoirs ◽  
Tight Gas Reservoirs ◽  
New Model ◽  
Irreducible Water Saturation

scholarly journals The Effect of Fracturing Fluid Saturation on Natural Gas Flow Behavior in Tight Reservoirs

Energies ◽  
2020 ◽  
Vol 13 (20) ◽  
pp. 5278
Author(s):  
Mianmo Meng ◽  
Yinghao Shen ◽  
Hongkui Ge ◽  
Xiaosong Xu ◽  
Yang Wu
Keyword(s):  
Gas Flow ◽  
Water Saturation ◽  
Flow Behavior ◽  
Tight Gas ◽  
Fracturing Fluid ◽  
Taiyuan Formation ◽  
Irreducible Water Saturation ◽  
Tight Reservoirs ◽  
The One ◽  
Median Pore

Hydraulic fracturing becomes an essential method to develop tight gas. Under high injection pressure, fracturing fluid entering into the formation will reduce the flow channel. To investigate the influence of water saturation on gas flow behavior, this study conducted the gas relative permeability with water saturation and the flow rate with the pressure gradient at different water saturations. As the two dominant tight gas-bearing intervals, the Upper Paleozoic Taiyuan and Shihezi Formations deposited in Ordos Basin were selected because they are the target layers for holding vast tight gas. Median pore radius in the Taiyuan Formation is higher than the one in the Shihezi Formation, while the most probable seepage pore radius in the Taiyuan Formation is lower than the one in the Shihezi Formation. The average irreducible water saturation is 54.4% in the Taiyuan Formation and 61.6% in the Shihezi Formation, which indicates that the Taiyuan Formation has more movable water. The average critical gas saturation is 80.4% and 69.9% in these two formations, respectively, which indicates that the Shihezi Formation has more movable gas. Both critical gas saturation and irreducible water saturation have a negative relationship with porosity as well as permeability. At the same water saturation, the threshold gradient pressure of the Taiyuan Formation is higher than the one in the Shihezi Formation, which means that water saturation has a great influence on the Taiyuan Formation. Overall, compared with the Shihezi Formation, the Taiyuan Formation has a higher median pore size and movable water saturation, but water saturation has more influence on its gas flow capacity. Our research is conducive to understanding the effect of fracturing fluid filtration on the production of natural gas from tight reservoirs.

A Water-Gas Relative Permeability Relationship for Tight Gas Sand Reservoirs

1990 ◽  
Vol 112 (4) ◽  
pp. 239-245 ◽  
Author(s):  
S. D. L. Lekia ◽  
R. D. Evans
Keyword(s):  
Capillary Pressure ◽  
Relative Permeability ◽  
Water Saturation ◽  
Gas Permeability ◽  
Tight Gas ◽  
Relative Permeabilities ◽  
The North ◽  
Tight Gas Sands ◽  
Straight Line ◽  
Phase Saturation

This paper presents a new approach for the analyses of laboratory-derived capillary pressure data for tight gas sands. The method uses the fact that a log-log plot of capillary pressure against water saturation is a straight line to derive new expressions for both wetting and nonwetting phase relative permeabilities. The new relative permeability equations are explicit functions of water saturation and the slope of the log-log straight line of capillary pressure plotted against water saturation. Relative permeabilities determined with the new expressions have been successfully used in simulation studies of naturally fractured tight gas sands where those determined with Corey-type expressions which are functions of reduced water saturation have failed. A dependence trend is observed between capillary pressure and gas permeability data from some of the tight gas sands of the North American Continent. The trend suggests that the lower the gas permeability, the higher the capillary pressure values at the same wetting phase saturation—especially for saturations less than 60 percent.

Assessment on Pore Structure of Western Sichuan Reservoir through Mercury Intrusion Porosimetry

2012 ◽  
Vol 226-228 ◽  
pp. 2082-2087
Author(s):  
Chi Guan ◽  
Zhang Hua Lou ◽  
Hai Jian Xie
Keyword(s):  
Pore Structure ◽  
Mercury Intrusion Porosimetry ◽  
Water Saturation ◽  
Absolute Permeability ◽  
Tight Gas ◽  
Gas Reservoir ◽  
Western Sichuan ◽  
Mercury Intrusion ◽  
Irreducible Water Saturation ◽  
Tight Gas Reservoir

Mercury intrusion porosimetry injection is important in assessing microscopic pore structure of reservoirs. This paper introduces an estimated function for investigating the pore characteristic of western Sichuan tight gas reservoir based on VG model. Better correlations between the measured and estimated results have been obtained using VG model. Representative parameters were obtained by fitting the predictions of VG model to the experimental data, and then the estimated formulation was proposed for the studied reservoir. Correlation analysis of the parameters of VG model confirms that absolute permeability and irreducible water saturation are important in mercury injection porosimetry. The approach applied in this paper is helpful in investigating tight reservoirs, especially in the common cases when measurement is difficult to carry out, partly because of complicated variability in the field, and partly because measuring is time-consuming and expensive.

Applications of Conventional Logs in Low Resistivity Contrast Tight Gas Reservoirs Identification

2013 ◽  
Vol 734-737 ◽  
pp. 41-44
Author(s):  
Xiao Peng Liu ◽  
Xiao Xin Hu ◽  
Xiao Ling Zhang ◽  
Rui Xu ◽  
Ling Ling Zhi
Keyword(s):  
Water Saturation ◽  
Total Porosity ◽  
Ratio Method ◽  
Tight Gas ◽  
Low Resistivity ◽  
Irreducible Water Saturation ◽  
The Difference ◽  
Tight Gas Formation ◽  
Conventional Logs ◽  
Gas Bearing

It’s a great challenge in identifying gas bearing formation from conventional logs in tight gas sandstones due to the low resistivity contrast caused by high irreducible water saturation. Based on the difference of the principles of three kinds of porosity logs (density, neutron and acoustic logs), three porosities difference method, three porosities ratio method, correlation of neutron and density logs and the overlap method of water-filled porosity and total porosity are introduced to identify tight gas bearing reservoirs. In gas bearing formations, the difference of three porosities is higher than 0.0, the ratio of three porosities is higher than 1.0, the correlation between density and neutron logs is negative, and the water filled porosities are lower than total porosities. On the contrary, in water saturated formations, the difference of three porosities is lower than 0.0, the ratio of three porosities is lower than 1.0, the correlation between density and neutron logs is positive, and the water filled porosities are overlapped with total porosities. Considering the complexity of in-suit formation, when the proposed identification criterion are mainly meet, the pore fluid should be determined, field examples show that the proposed techniques are applicable in tight gas formation identification.

An Integrated Petrophysical Characterization of a Siliciclastic Tight Gas Reservoir in Neuquén Basin, Western Argentina

2021 ◽  
Vol 62 (6) ◽  
pp. 711-736
Author(s):  
Nicolas Carrizo ◽  
◽  
Emiliano Santiago ◽  
Pablo Saldungaray ◽  
◽  
...  
Keyword(s):  
Water Saturation ◽  
Seismic Inversion ◽  
Tight Gas ◽  
Analysis Model ◽  
Throat Radius ◽  
Field Development ◽  
Drilling Rig ◽  
Irreducible Water Saturation ◽  
Tight Gas Reservoir ◽  
Pulsed Neutron

The Río Neuquén Field is located between Neuquén and Río Negro provinces, Argentina. Historically, it has been a conventional oil producer, but it was converted to a tight gas producer from deeper reservoirs. The targeted geological formations are Lajas, which is already a known tight gas producer, and the less-known overlaying Punta Rosada Formation, which is the main objective of the current work. Punta Rosada presents a diverse lithology, including shaly intervals separating multiple stacked reservoirs that grade from fine-grained sandstones to conglomerates. The reservoir pressure can change from the normal hydrostatic gradient to up to 50% of overpressure. There is little evidence of movable water. The key well in this study has a comprehensive set of openhole logs, including pulsed-neutron spectroscopy data, and is supported by a full core study over 597 ft. Additionally, data from several offset wells were used, containing sidewall cores and complete sets of electrical logs. This allowed the development of rock-calibrated mineral models, adjusting the clay volume with X-ray diffraction data, porosity, and permeability with core measurements, and linking the log interpretation to dominant pore-throat radius models from MICP Purcell tests. Several water saturation models were tested, attempting to adjust the irreducible water saturation with NMR and Purcell tests at reservoir conditions. As a result, three hydraulic units were defined and characterized, identifying a strong correlation with lithofacies observed in cores and image logs. A cluster analysis model allowed the propagation of the facies to the rest of the wells (50). Finally, lithofacies were distributed in a full-field 3D model, guided by an elastic seismic inversion. In the main key well, in addition to the openhole logs and core data, a casedhole pulsed-neutron log (PNL) was also acquired, which was used to develop algorithms to generate synthetic pseudo-openhole logs such as bulk density and resistivity, integrated with the spectroscopy mineralogical information and other PNL data, to perform the petrophysical evaluation. This enables the option to evaluate wells in contingency situations where openhole logs are not possible or too risky, and also in planned situations to replace the openhole data in infill wells, saving considerable drilling rig time during this field development phase. Additionally, the calibrated casedhole model can be used in old wells. This paper explores the integration of different core and log measurements and explains the development of rock-calibrated petrophysical and rock type models addressing the characterization challenges found in tight gas sand reservoirs. The results of this study will be crucial to optimize the field development.

A Complete Petrophysical-Evaluation Method for Tight Formations From Drill Cuttings Only in the Absence of Well Logs

SPE Journal ◽  
2013 ◽  
Vol 19 (04) ◽  
pp. 636-647 ◽  
Author(s):  
Camilo Ortega ◽  
Roberto Aguilera
Keyword(s):  
Evaluation Method ◽  
Water Saturation ◽  
Horizontal Wells ◽  
Well Logs ◽  
Tight Gas ◽  
Drill Cuttings ◽  
Irreducible Water Saturation ◽  
Tight Formations ◽  
Porosity And Permeability ◽  
Petrophysical Evaluation

Summary The amount of tight-formation petrophysical work conducted at present in horizontal wells and the examples available in the literature are limited to only those wells that have complete data sets. This is very important. But the reality is that in the vast majority of horizontal wells, the data required for detailed analyses are quite scarce. Petrophysical evaluation in the absence of well logs and cores can now be considered owing to the possibility of measuring both the permeability and porosity of drill cuttings. This is essential because the application of the successive correlations used throughout the paper is based on porosity and permeability data. To try to alleviate the data-scarcity problem, a new method is presented for complete petrophysical evaluation derived from information that can be extracted from drill cuttings in the absence of well logs. The cuttings data include porosity and permeability. The gamma ray and any other logs, if available, can help support the interpretation. However, the methodology is built strictly on data extracted from cuttings and can be used for horizontal, slanted, and vertical wells. The method is illustrated with the use of a tight gas formation in the Deep basin of the western Canada sedimentary basin (WCSB). However, it also has direct application in the case of liquids. The method is shown to be a powerful petrophysical tool because it allows quantitative evaluation of water saturation, pore-throat aperture, capillary pressure, flow units, porosity (or cementation) exponent m, true-formation resistivity, and distance to a water table (if present). Also, the method allows one to distinguish the contributions from viscous and diffusion-like flow in tight gas formations. The method further allows the construction of Pickett plots without previous availability of well logs, and it assumes the existence of intervals at irreducible water saturation, which is the case of many tight formations currently under exploitation. It is concluded that drill cuttings are a powerful direct source of information that allows complete and practical evaluation of tight reservoirs in which well logs are scarce. The uniqueness and practicality of this quantitative procedure originate from the fact that it starts only from the laboratory analysis of drill cuttings—something that has not been performed in the past.

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