Advances in Cased-Hole Formation Evaluation—The Access to Untapped Tight-Gas Resources in Mature Fields: A Case Study from the Dnieper-Donets Basin, Ukraine

2021 ◽  
Author(s):  
Rafael Zambrano ◽  
Yevhen Makar ◽  
Michael Sadivnyk ◽  
Andriy Butenko ◽  
Oleksandr Doroshenko ◽  
...  
Keyword(s):  
Matrix Effects ◽  
Gas Production ◽  
Volume Estimation ◽  
Advanced Technology ◽  
Donets Basin ◽  
Neutron Spectroscopy ◽  
Tight Gas ◽  
Formation Evaluation ◽  
Pulsed Neutron ◽  
Low Porosity

Abstract The Sakhalin Field is located in the Dnieper-Donets Basin, east of Ukraine, and has been producing 7.7 billion cubic meters of natural gas in place from carboniferous rocks since the 1980s. Notwithstanding, it is strongly believed that significant untapped resources remain in the field, specifically those classified as tight intervals. Advances in wireline logging technology have brought, besides better accuracy on measurements behind the casing, a new measurement called fast neutron cross-section (FNXS), which has proved to be sensitive enough to the volume of gas in low-porosity formations. This enabled a quantitative interpretation for a better understanding of where these additional resources may lie in the Sakhalin Field. The methodology is based on advanced pulsed neutron spectroscopy logs to assess the essential formation properties such as lithology, porosity, and gas saturation and reduce the evaluation uncertainty in potential tight gas intervals. The advanced technology combines measurements from multiple detectors that represent independent formation properties such as formation sigma, thermal neutron porosity, FNXS, and elemental fractions. To address the lithology, the tool measures directly the rock elements required to determine representative mineralogy and matrix properties, which in turn are used to compensate for the matrix effects and obtain a reliable porosity and gas volume estimation. The methodology was tested on the upper Visean productive zones (Mississippian epoch) characterized by its low porosity (<10 pu) and permeability (<10 mD). In the past, those intervals have been overlooked because of inconclusive petrophysical interpretation based on basic openhole logs and their low production in some areas of the field. The necessity to finding new reserves has motivated the re-evaluation of possible bypassed tight-gas intervals by logging of mature wells behind casing in different sectors of the field. Advanced pulsed neutron spectroscopy logging behind casing uniquely identifies reserves in tight-gas intervals where basic open-hole interpretations were ambiguous. The gas production obtained from the perforated intervals supports the formation evaluation parameters estimated from the standalone interpretation of the pulsed neutron data. This work describes in detail the application of the alternative methodology and interpretation workflow to evaluate the formation through the casing. A concrete example is presented to illustrate the effectiveness of this approach in the revealing and development of tight gas reservoirs in mature fields in the Dnieper-Donets Basin.

Open- and Cased- Hole Formation Evaluation Workflows Running Together for Reducing Uncertainties in Gas Reservoirs: An Acquisition Data and Evaluation Strategy in Dnieper-Donets Basin, Ukraine

2021 ◽  
Author(s):  
Rafael Zambrano ◽  
Michael Sadivnyk ◽  
Yevhen Makar ◽  
Chiara Cavalleri ◽  
David Rose
Keyword(s):  
Magnetic Resonance ◽  
Donets Basin ◽  
Neutron Spectroscopy ◽  
Petrophysical Properties ◽  
Hole Formation ◽  
Gas Reservoirs ◽  
Formation Evaluation ◽  
Open Hole ◽  
Pulsed Neutron ◽  
Evaluation Techniques

Abstract Formation evaluation using cased-hole logs is a primary option for re-evaluating old wells in brownfields or contingency logging in new wells. Its consistency with a robust open hole evaluation is vital for its future implementation in field development. This work describes detailed open- and cased- hole evaluation workflows integrating different advanced subsurface measurements and alternative interpretation techniques to reduce the uncertainties of deriving the main petrophysical properties across the conventional and tight gas reservoirs in the Dnieper-Donets basin. Since not all open-hole measurements can be recorded behind casing and some of the cased hole logs are not characterized for open hole conditions, it is not always possible to implement the same evaluation techniques for measurements done in open hole and cased hole. Nevertheless, different measurements provide different formation responses that supplement their gaps from one another. A wireline data acquisition strategy has been elaborated to carry out formation evaluation workflows using open- and cased-hole data independently but learning from each other. The methodology is based on novel and non-standard evaluation techniques that use measurements from advanced wireline technology such as nuclear magnetic resonance (NMR) and advanced pulsed neutron spectroscopy logs. The methodology was applied to log data recorded on the Visean and Serpukhovian (Lower Carboniferous) productive gas zones, characterized by porosity (5-15pu) and permeability (0.1-100mD). The principal challenge for the formation evaluation of these reservoirs is deriving an accurate estimation of porosity, which requires removing the gas and matrix effects on the log responses. An inaccurate porosity estimation will result in an inaccurate permeability and water saturation, and the problem worsens in low-porosity rocks. In the open hole, the porosity computation from the Density-Magnetic Resonance (DMR) technique has proven to be more accurate in comparison with common single porosity methods. The same problem is addressed in cased hole conditions with the advanced pulsed neutron spectroscopy logs and a novel technique that combines the thermal neutron elastic scattering and fast neutron cross sections to obtain a gas-free and matrix-corrected porosity, as well as a resistivity independent gas saturation. The consistency of petrophysical properties independently estimated from the two separate workflows add confidence to the approach, and this is reflected in the gas production obtained from the perforated intervals. This script describes in detail the open- and cased- hole formation evaluation workflows and the wireline technology and methodologies applied. Actual examples illustrate the effectiveness of these quantitative approaches in the Dnieper-Donets basin.

Logging Optimization and Data Analysis Enabling Bypass Pay Identification and Hydrocarbon Quantification with Advanced Pulsed Neutron Behind Casing

2021 ◽  
Author(s):  
Sviatoslav Iuras ◽  
Samira Ahmad ◽  
Chiara Cavalleri ◽  
Yernur Akashev
Keyword(s):  
Cross Section ◽  
Pore Space ◽  
High Energy ◽  
Elastic Cross Section ◽  
Gas Production ◽  
Donets Basin ◽  
Lithology Identification ◽  
Open Hole ◽  
Pulsed Neutron

Abstract Ukraine ranks the third largest gas reserves in Europe. Gas production is carried out mainly from the Dnieper-Donets Basin (DDB). A gradual decline in reserves is forcing Ukraine to actively search for possible sources to increase reserves by finding bypassed gas intervals in existing wells or exploration of new prospects. This paper describes 3 case studies, where advanced pulsed neutron logging technology has shown exceptional value in gas-bearing layer identification in different scenarios. The logging technology was applied for formation evaluation. The technology is based on the neutron interaction with the minerals and the fluids contained in the pore space. The logging tool combines measurements from multiple detectors and spacing for self-compensated neutron cross-capture section (sigma) and hydrogen index (HI), and the Fast Neutron Cross Section (FNXS) high-energy neutron elastic cross section rock property. Comprehensive capture and inelastic elemental spectroscopy are simultaneously recorded and processed to describe the elemental composition and the matrix properties, reducing the uncertainties related to drilling cuttings analysis, and overall, the petrophysical evaluation combined with other log outputs. The proposed methodology was tested in several wells, both in open hole and behind casing. In the study we present its application in three wells from different fields of the DDB. The log data acquisition and analysis were performed across several sandstone beds and carbonates formation with low porosities (<10%), in various combinations of casing and holes sizes. The results showed the robustness and effectiveness of using the advanced pulsed neutron logging (PNL) technologies in multiple cases: Case Study A: Enabling a standalone cased hole evaluation and highlighting new potential reservoir zones otherwise overlooked due to absence of open hole logs. Case Study B: Finding by-passed hydrocarbon intervals that were missed from log analysis based on conventional open hole logs for current field operator. Case Study C: Identifying gas saturated reservoirs and providing solid lithology identification that previously was questioned from drilling cuttings in an unconventional reservoir.

QUANTIFYING BITUMEN PLUGGING IN TIGHT GAS RESERVOIR USING NMR AND PULSED-NEUTRON SPECTROSCOPY LOGGING

2019 ◽  
Author(s):  
Azzan Al-Yaarubi ◽  
Khalsa Al-Hadidi ◽  
Rinat Lukmanov ◽  
Ali Al-Mahrouqi ◽  
Marcel Elie
Keyword(s):  
Neutron Spectroscopy ◽  
Tight Gas ◽  
Gas Reservoir ◽  
Tight Gas Reservoir ◽  
Pulsed Neutron

Exploiting Slim Pulsed Neutron Spectroscopy for Unlocking Reservoir Potential in Brownfields: Two Examples from Gulf of Suez Offshore Field in Egypt

2021 ◽  
Author(s):  
Mohamed Ameen ◽  
Eslam Atwa ◽  
Youssif Youssif ◽  
Emad Abdel Hakim ◽  
Mohamed Farouk ◽  
...  
Keyword(s):  
Integrated Approach ◽  
Carbonate Reservoir ◽  
Advanced Technology ◽  
Gulf Of Suez ◽  
Neutron Spectroscopy ◽  
Fluid Saturation ◽  
Crucial Information ◽  
Hydrocarbon Saturation ◽  
Cement Integrity ◽  
Pulsed Neutron

Abstract For more than 40 years, pulsed neutron spectroscopy has been primarily used in reservoir management to determine hydrocarbon saturation profiles, tracking reservoir depletion, and planning workover activities to diagnose production problems such as water influx. Legacy pulsed neutron tools used to provide this information for more than four decades, but they were challenged when a mixed lithology reservoir is encountered, complex completions, unknown borehole conditions, and poor cement integrity in cased boreholes. This paper presents two successful field examples and applications using the advanced slim pulsed neutron spectroscopy to precisely determine multiphase contacts in a complex geological structure, provide current hydrocarbon saturation independent of the quality of cement behind the casing, and identifying bypassed hydrocarbon. This was of paramount importance in understanding current reservoir fluid distribution to reveal the true potential of this offshore brownfield located in the Gulf of Suez, Egypt. An integrated approach and candidate well selection were done that resulted in selecting two candidate wells that had poor cement quality behind casing, heterogeneous carbonate reservoir with mixed lithology, and uncertain fluid contacts in a complex reservoir structure. These combined borehole and reservoir conditions resemble challenges for capturing this crucial information with high confidence using the legacy pulsed neutron tool, and therefore required an advanced technology that can overcome these challenges using a single logging mode at twice the logging speed of any current pulsed neutron technology available in the industry. Based on the results, a workover campaign was implemented in this mature field to increase overall oil production with very efficient cost control, especially with this unprecedented time the O&G industry is going through. An integrated approach was set that resulted in the selection of two wells for the saturation determination logging tool deployment. Detailed high-resolution mineralogy, self-compensated total porosity and sigma, fluid type identification, and multiphase fluid saturation was obtained with high precision behind cased borehole independent of cement integrity and borehole fluid reinvasion. The results provided crucial information as an input to the integrated reservoir engineering approach which revealed around a 100-m net oil interval which was previously overlooked due to relatively low resistivity. Besides, fluids contacts were evaluated that confirmed the development of a secondary gas cap and the water encroachment direction. This technology can be further applied to more brownfields provided the right candidate selection is done to understand the potentiality of the field which would increase the recovery factor of the brownfields that represent almost more than 65% of the oil and gas fields around the world.

Multidetector Pulsed-Neutron Tool Application in Low-Porosity Reservoir–A Case Study in Mutiara Field, Indonesia

2020 ◽  
Vol 61 (6) ◽  
pp. 623-632
Author(s):  
Aditya Arie Wijaya ◽  
◽  
Rama Aulianagara ◽  
Weijun Guo ◽  
Fetty Maria Naibaho ◽  
...  
Keyword(s):  
Dynamic Range ◽  
New Technology ◽  
Gas Production ◽  
Production Test ◽  
Gas Saturation ◽  
The Third ◽  
High Dependency ◽  
Low Dynamic Range ◽  
Pulsed Neutron ◽  
Low Porosity

In mature fields, pulsed-neutron logging is commonly used to solve for the remaining saturation behind the casing. For years, sigma-based saturation has been used to calculate gas saturation behind casing; however, the high dependency of sigma-to-water salinity of the formation, especially the low-dynamic range at porosity near 12 p.u., has proven to be challenging in low-porosity gas rock. A new measurement from the third detector from a multidetector pulsed-neutron tool (MDPNT) is proposed to provide a better estimation of the gas saturation in a low-porosity reservoir. Two sets of independently measured sigma and the third detector were taken in a casedhole well, with a dual-tubing system of a long string and short string. For the third-detector measurement, the measurement was based on the ratio of the slow capture gate and inelastic gate component from the decay curve created by the long detector. This ratio can be used to detect gas in a tight reservoir with a minimum salinity and lithology effect. This data will then be used to calculate the gas saturation from the third detector, and the result is compared to sigma-based gas saturation. At an interval where the porosity is above 12 p.u., the sigma-based gas saturation and MDPNT-based gas saturation are very much in agreement. However, in a low-porosity reservoir near 12 p.u. or below, the sigma-based measurement starts to show its limitation. Meanwhile, the MDPNT-based gas saturation clearly shows the remaining gas saturation where sigma-based measurements failed to detect it. The subsequent decision was made based on the log analysis result, and perforation was done at a potential interval based on the MDPNT result. The results from the production test confirm the MDPNT-based gas saturation with 700-Mscf/d gas production added. This study showcases a new technology to solve a low-porosity gas reservoir issue where a sigma-based measurement underestimates the remaining gas saturation. Using two different measurements in the same well, the results from the MDPNT measurement demonstrated a better result compared to the sigma-based measurement in low-porosity rock

Unlocking Potential in Thinly Laminated Reservoirs Through Cased Hole Pulsed Neutron Logging

2021 ◽  
Author(s):  
Yernur Akashev ◽  
Samira Ahmad ◽  
Chiara Cavalleri ◽  
Yulia Ignatochkina ◽  
Yevgenii Solodkiy
Keyword(s):  
High Resolution ◽  
Advanced Technology ◽  
Donets Basin ◽  
Hole Density ◽  
Log Data ◽  
Physical Measurements ◽  
Lithology Identification ◽  
Neutron Porosity ◽  
Pulsed Neutron ◽  
Very High

Abstract Field A is located in the center of the Dnieper-Donets basin (DDB), producing gas from clastic reservoirs from several deep horizons in the Upper Visean sediments. The case study highlights the application of advanced pulsed neutron logging technologies and high-resolution data processing to unlock the sedimentary layers’ characteristics and the gas potential behind the casing. Multiple rock measurements are simultaneously recorded for continuous lithology identification, porosity quantification, and differentiating gas-filled porosity from low porosity formations. Dedicated log data acquisition and processing techniques enable investigating the effect of thin laminations on reservoir quality and producibility. The use of advanced pulsed neutron logging and interpretation method reduces the operational risks while securing critical reservoir parameters. A pulsed neutron spectroscopy tool provided a rich dataset including a self-compensated sigma and neutron porosity logs, fast neutron cross section (FNXS) together with capture and inelastic elemental spectroscopy. The logs interpretation was performed integrating FNXS and very high-resolution neutron porosity with mineral dry weight fractions and matrix properties from elemental spectroscopy processing. The comparison between the pulsed neutron measurements with standard open hole logs highlights the critical role of advanced fit-to-purpose logging techniques to accurately describe the underlying complexity of the formation and obtain improved net reservoir and net pay thicknesses in laminated and heterogeneous sequences. The logging objectives were successfully met, and additional valuable information related to the reservoir were determined in an efficient manner. The study also shows the critical value of FNXS as confident gas measurement. The FNXS measures the ability of the formation interacting with fast neutrons which are highly dependent on atomic density and not dominated by particular isotopes such as traditional sigma and porosity measurements. It is highly sensitive to gas-filled porosity, but it is independent of hydrogen index, acting like a cased-hole density measurement. Moreover, it demonstrates the importance of accurate knowledge of the mineralogy and matrix as well as the ability to measure at very high resolution to unravel the highly layered nature of the formation and its implication on completion and production strategy. Pulsed neutron logging has evolved over a half century, but the intrinsic physical measurements remain unchanged. With the advent and introduction of the new FNXS measurement and a high-quality spectroscopy elemental concentration, a higher quality measurement and interpretation can be obtained from standalone pulsed neutron logging. The advanced technology and log data analysis interpretation module can be considered as an effective and comprehensive methodology for robust formation evaluation in similar and complex setting.

Challenges to Geosteering and Completion Optimization of Horizontal Wells in the Cotton Valley Formation, East Texas

2015 ◽  
Vol 18 (04) ◽  
pp. 590-598
Author(s):  
S.. Liu ◽  
J. L. Lucas ◽  
P. A. Plemons ◽  
X.. Zhou ◽  
A.. Zett ◽  
...  
Keyword(s):  
Hydraulic Fracturing ◽  
Rock Type ◽  
Horizontal Wells ◽  
Gas Production ◽  
Tight Gas ◽  
East Texas ◽  
Log Data ◽  
Formation Evaluation ◽  
Tight Gas Sands ◽  
Cotton Valley

Summary Cotton Valley tight gas sands in the East Texas basin of North America consist of very-fine-grained, well-sorted quartz arenites and subarkoses that are overprinted by significant diagenetic processes. Stratigraphic variations in rock type control gas production. Hydraulic fracturing delivers economic gas production. We drilled horizontal wells more than 4,000 ft long consisting of more than 12 hydraulic-fracturing stages. The good gas-producing rock-type reservoirs are usually less than 14-ft thick and exhibit strong diagenetic overprint. Low gas prices challenge the use of sophisticated geosteering logs. By use of a very-basic gamma ray (GR) log and very-limited offset-pilot-well data, chasing such thin and variable sand bodies over a distance of 4,000 ft in a marginal marine sedimentary environment is daunting. Apart from this, horizontal wells that target thin layers present unique challenges to completion optimization. We acquired quad-combo log data, including azimuthal-density image data, by use of a logging-while-drilling (LWD) tool. We performed extensive log modeling by combining the horizontal well logs with logs from the two offset vertical wells, and achieved consistent interpretation. Log modeling has helped the post-drill well diagnosis in geosteering, completion design, and production performance. It has also supported formation evaluation. This study will highlight an integrated-study work flow in tight gas sands by use of openhole and cased-hole data. It will demonstrate the geosteering challenges, explain the log-modeling process, and display the formation-evaluation results. Geomechanical study, together with hydraulic-fracturing data and production-log data, will be used to confirm that good gas-producing rock types are easier to fracture, and they contribute better to production.

Data Acquistion and Formation Evaluation Strategies in Anistrospic, Tight Gas Reservoirs

2008 ◽  
Author(s):  
Hans de Koningh ◽  
Bernd Heinrich Herold ◽  
Koksal Cig ◽  
Fahd Ali ◽  
Sultan Mahruqy ◽  
...  
Keyword(s):  
Tight Gas ◽  
Gas Reservoirs ◽  
Tight Gas Reservoirs ◽  
Formation Evaluation ◽  
Evaluation Strategies ◽  
Data Acquistion

SELF-COMPENSATED CASED-HOLE PULSED NEUTRON SPECTROSCOPY MEASUREMENTS

2020 ◽  
Author(s):  
Tong Zhou ◽  
◽  
David Rose ◽  
Jeffrey Miles ◽  
Jason Gendur ◽  
...  
Keyword(s):  
Neutron Spectroscopy ◽  
Pulsed Neutron

Natural fractures in tight gas sandstones: a case study of the Upper Triassic Xujiahe Formation in Xinchang gas field, Western Sichuan Basin, China

2021 ◽  
pp. 1-18
Author(s):  
Yunzhao Zhang ◽  
Lianbo Zeng ◽  
Wenya Lyu ◽  
Dongsheng Sun ◽  
Shuangquan Chen ◽  
...  
Keyword(s):  
Production Capacity ◽  
Gas Production ◽  
Upper Triassic ◽  
Tight Gas ◽  
Natural Fractures ◽  
Carbon And Oxygen Isotopes ◽  
Gas Field ◽  
Xujiahe Formation ◽  
Western Sichuan ◽  
Tight Gas Reservoir

Abstract The Upper Triassic Xujiahe Formation is a typical tight gas reservoir in which natural fractures determine the migration, accumulation and production capacity of tight gas. In this study, we focused on the influences of natural fractures on the tight gas migration and production. We clarified characteristics and attributes (i.e. dips, apertures, filling degree and cross-cutting relationships) of the fractures based on image logging interpretations and core descriptions. Previous studies of electron spin resonance, carbon and oxygen isotopes, homogenization temperature of fluid inclusions analysis and basin simulation were considered. This study also analysed the fracture sequences, source of fracture fillings, diagenetic sequences and tight gas enrichment stages. We obtained insight into the relationship between fracture evolution and hydrocarbon charging, particularly the effect of the apertures and intensity of natural fractures on tight gas production. We reveal that the bedding fractures are short horizontal migration channels of tight gas. The tectonic fractures with middle, high and nearly vertical angles are beneficial to tight gas vertical migration. The apertures of fractures are controlled by the direction of maximum principal stress and fracture angle. The initial gas production of the vertical wells presents a positive correlation with the fracture abundance, and the intensity and aperture of fractures are the fundamental factors that determine the tight gas production. With these findings, this study is expected to guide the future exploration and development of tight gas with similar geological backgrounds.

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