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Collaborating Authors
Unconventional gas resources con-tinue to be a growing part of the total gas production in the United States and have captured the interest of energy firms around the world. Unconventional resources comprise three major categories; tight-gas sand-stones (low-permeability), shale gas, and coal-bed methane. Tight-gas reservoirs currently comprise approx-imately 35% of the uncon-ventional gas production in the U.S. Lower 48 (Wood Mackenzie's Unconventional Gas Service).
- North America > United States > Wyoming > Sand Wash Basin (0.99)
- North America > United States > Wyoming > Green River Basin (0.99)
- North America > United States > Wyoming > Greater Green River Basin > Wamsutter Basin > Wamsutter Field (0.99)
- (4 more...)
An improved method to characterize the full-scale pore system and dual pore model of tight sands
Zhu, Yurui (Chengdu University of Technology) | Lu, Zhengyuan (Chengdu University of Technology) | Feng, Mingshi (Chengdu University of Technology) | Wang, Jun (Exploration and Development Research Institute of Shengli Oilfield) | Li, Zhipeng (Exploration and Development Research Institute of Shengli Oilfield)
Abstract Tight sands have pore systems with complex structures and widely distributed pore sizes. We have studied the characteristics of these pore systems to better understand their important role in the accumulation and migration mechanisms of oil and gas reservoirs, which may enhance our ability to evaluate reservoir quality and predict reservoir production. To this end, we carried out thin-section analysis, scanning electron microscopy, pressure-controlled porosimetry (PCP), and rate-controlled porosimetry (RCP) to describe the pore systems of a typical tight-sand reservoir in East Asia. We improved a differential-distribution-based splicing method to reveal the full-scale pore systems using PCP and RCP. We found that the typical pore radius distribution in our target reservoir exhibits two peaks: at radius and at radius . Based on pore shapes and connections, intergranular pores are network structures and clay-host pores are tree-like structures. Intragranular pores, in contrast, can be different structures under different conditions. If wide throats are present, intragranular pores function as typical tree-like pores; if throats are narrow, they serve as the pore parts of a network-pore system. Network pores are the primary contributors to porosity and permeability, whereas tree-like pores mainly contribute to porosity. In some high-clay sands, however, the tree-like pores may also contribute to permeability. Based on their fractal characteristics, we divided the pore systems of tight sands into three types: (1)Â a network-structure-controlled intergranular pore system, (2)Â a tree-like-structure-controlled clay-host pore system, and (3)Â a network-structure-controlled intergranular-intragranular pore system.
- North America > United States > North Dakota (0.46)
- Asia > China > Shandong Province (0.29)
- North America > Canada > Saskatchewan (0.28)
- (2 more...)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Sandstone (1.00)
- Geology > Mineral > Silicate > Phyllosilicate (1.00)
- Geology > Geological Subdiscipline (1.00)
- Oceania > Australia > Western Australia > Perth Basin > Carynginia Shale Formation (0.99)
- North America > United States > South Dakota > Williston Basin (0.99)
- North America > United States > Montana > Williston Basin (0.99)
- (17 more...)
- Reservoir Description and Dynamics > Unconventional and Complex Reservoirs > Shale gas (1.00)
- Reservoir Description and Dynamics > Reservoir Fluid Dynamics > Flow in porous media (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Exploration, development, structural geology (1.00)
- Reservoir Description and Dynamics > Formation Evaluation & Management (1.00)
Abstract Pay in tight-rock reservoirs is often associated with organic richness. The assumption is that the low permeabilities of the source rock do not allow for the migration of the hydrocarbon generated during the thermal maturation process. If core data are available, the water saturation, porosity, and total organic carbon (TOC) measurements can be used to confirm that the resource in place is correlated with the organic matter, which impacts the log characterization of pay. We studied the Wolfcamp A, Wolfcamp C, and Wolfcamp D tight-rock reservoirs using seven wells with core data through the Delaware Basin Wolfcamp Formation and discussed appropriate log-based pay identification methods. The linear relationship between TOC and original hydrocarbon in place (OHIP) for samples in the Wolfcamp C and D intervals validated the hypothesis of a self-sourced reservoir. We adopted the well-established correlation between TOC and formation bulk density to identify the better part of the Wolfcamp C and D reservoirs. Our core data suggested to use a bulk density of or less to define pay. The lack of trend in the scatterplot of TOC and OHIP for samples in the Wolfcamp A interval indicated that the hydrocarbon had probably migrated, at least on a local scale. In this case, pay could not be identified by log techniques developed to calculate TOC in organic-rich rocks. Instead, we built an OHIP model based on a quad combo logging suite using an ensemble learning method. This model favorably compared with a TOC-based pay flag against production logging data from two vertical producers with stages through the Wolfcamp A interval.
- North America > United States > Texas (1.00)
- North America > United States > New Mexico (1.00)
- Geology > Structural Geology > Tectonics > Compressional Tectonics > Fold and Thrust Belt (0.68)
- Geology > Geological Subdiscipline > Economic Geology > Petroleum Geology (0.67)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Mudrock > Shale (0.30)
- Energy > Oil & Gas > Upstream (1.00)
- Government > Regional Government > North America Government > United States Government (0.47)
- North America > United States > Texas > Permian Basin > Yeso Formation (0.99)
- North America > United States > Texas > Permian Basin > Yates Formation (0.99)
- North America > United States > Texas > Permian Basin > Wolfcamp Formation (0.99)
- (28 more...)
ABSTRACT Petrophysical rock classification is an important component of the interpretation of core data and well logs acquired in complex reservoirs. Tight-gas sandstones exhibit large variability in all petrophysical properties due to complex pore topology resulting from diagenesis. Conventional methods that rely dominantly on hydraulic radius to classify and rank reservoir rocks are prone to rock misclassification at the low-porosity and low-permeability end of the spectrum. We introduce a bimodal Gaussian density function to quantify complex pore systems in terms of pore volume, major pore-throat radii, and pore-throat radius uniformity. We define petrophysical dissimilarity (referred to as orthogonality) between two different pore systems by invoking the classic “bundle of capillary tubes” model and subsequently classify rocks by clustering an orthogonality matrix constructed with all available mercury injection capillary pressure data. The new method combines several rock textural attributes including porosity, pore-throat radius, and tortuosity for ranking reservoir rock quality in terms of flow capacity. We verify the new rock classification method with field data acquired in the Cotton Valley tight-gas sandstone reservoir located in the East Texas basin. The field case shows that the new method consistently identifies and ranks rock classes in various petrophysical data domains, including porosity-permeability trends, pore-size distribution, mercury injection capillary pressure, and NMR transverse relaxation time () spectra. Relative permeability curves, which are difficult to measure in the laboratory for tight rocks, are quantified with Corey-Burdine’s model using the bimodal Gaussian pore-size distribution and are validated with core data.
Tight gas is the term commonly used to refer to low permeability reservoirs that produce mainly dry natural gas. Many of the low permeability reservoirs that have been developed in the past are sandstone, but significant quantities of gas are also produced from low permeability carbonates, shales, and coal seams. Production of gas from coal seams is covered in a separate chapter in this handbook. In this chapter, production of gas from tight sandstones is the predominant theme. However, much of the same technology applies to tight carbonate and to gas shale reservoirs.
- North America > United States > Texas (1.00)
- Europe (1.00)
- Asia (1.00)
- North America > United States > Colorado (0.67)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Mudrock > Shale (0.69)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Sandstone (0.68)
- North America > United States > Texas > Travis Peak Formation (0.99)
- North America > United States > Texas > East Texas Salt Basin > Whelan Lease > Waskom Field > Lowe Paluxy Formation (0.99)
- North America > United States > Texas > East Texas Salt Basin > Cotton Valley Group Formation (0.99)
- (38 more...)