This paper was prepared for presentation at the Unconventional Resources Technology Conference held in Houston, Texas, USA, 23-25 July 2018. The URTeC Technical Program Committee accepted this presentation on the basis of information contained in an abstract submitted by the author(s). The contents of this paper have not been reviewed by URTeC and URTeC does not warrant the accuracy, reliability, or timeliness of any information herein. All information is the responsibility of, and, is subject to corrections by the author(s). Any person or entity that relies on any information obtained from this paper does so at their own risk.
Recently, the miscible CO2-EOR tertiary process used in the main pay zone (MP) of suitable reservoirs has broadened to include exploitation of the underlying residual oil zone (ROZ) where a significant amount of oil may remain. The objective of this study is to identify the ROZ and to assess the remaining oil in a brownfield ROZ by using core data and conventional well logs with probabilistic and predictive methods.
Core and log data from three wells located in the East Seminole Field in Gaines County, Texas, were used to identify the MP and ROZ in the San Andres Limestone, and to predict oil saturations. The core measurements were used to calculate probabilistic in-situ oil saturations within the MP and the ROZ as a function of depth. Well logs, in combination with core data and calculated saturations, on the other hand, were used to develop two expert systems using artificial neural networks (ANN); one to identify the ROZ and MP, and the other to predict oil saturation. These systems were also supported by a classification and regression tree (CART) analysis to delineate the rules that lead to classifications of zones.
Results showed that expert systems developed and calibrated by combining core and well log data can identify MP and ROZ with a success score of more than 90%. Saturations within these zones can be predicted with a correlation coefficient of around 0.6 for testing and 0.8 for training data. The analyses showed that neutron porosity and density well log readings are the most influential ones to identify zones in this field and to predict oil saturations in the MP and ROZ. To explain the relationships of input data with the results, a rule-based system was also applied, which revealed the underlying petrophysical differences between MP and ROZ.
This new predictive approach using machine learning techniques, could potentially address the challenges that previous studies have come up against in defining the ROZ within the formation and quantifying remaining oil saturations. The method can potentially be applied to additional fields and help reliably identify the ROZ and estimate saturations for future resource evaluations.
Wilson, Thomas (West Virginia University) | Kavousi, Payam (West Virginia University) | Carr, Timothy (West Virginia University) | Carney, Brooke (Northeast Natural Energy LLC) | Uschner, Natalie (Schlumberger) | Magbagbeola, Oluwaseun (Schlumberger) | Xu, Lili (Schlumberger)
Inversion of 3D-3C data yields P- and S-acoustic impedances that can be combined to yield λρ and μρ (e.g. Goodway et al., 1997; Hampson et al., 2005; Russell, 2014; Sayers et al., 2015). λ and μ, Lamè's parameters, represent incompressibility and shear modulus, respectively. Interpretation of λρ-μρ volumes has been used recently to evaluate unconventional oil and gas shale reservoirs (see Alzate, 2012; Alzate and Devegowda, 2013; and Perez and Marfurt, 2014 and 2015). Alzate and Devegowda (2013) use λρ-μρ crossplots to identify organic rich and brittle sweet spots. They also associate lower Young's modulus with more organic rich intervals and lower Poisson's ratio with more brittle intervals.
In this study we compute λρ-μρ from log data for the Middle Devonian Hamilton Group and bounding Tully and Onondaga limestones taken from the vertical pilot well (Figure 1) drilled by Northeast Natural Energy, LLC on their Morgantown, WV well pad. We also compute brittleness using approaches proposed by Greiser and Bray (2007), Jarvie et al. (2007) and Wang and Gale (2009). We then note the results of a stimulation test and consider hydraulic fracture development within the context of these log derived parameters and mechanical properties. The stimulation tests are conducted using a geomechanical model developed from a comprehensive suite of logs collected in the vertical pilot well by Schlumberger (see Wilson et al., 2016).
Results indicate that the TOC (total organic carbon) rich Marcellus Shale is associated with lower Young's modulus, Poisson's ratio and lower values of λρ and μρ. High TOC intervals tend to be more brittle using both the Jarvie et al. (2007) and Wang and Gale (2009) approaches; however, brittle intervals are not confined to TOC rich zones. Model hydraulic fractures are, however, generally confined to TOC rich strata, while microseismic activity associated with shear failure of pre-existing natural fractures during treatment is distributed through the Hamilton Group.
Presentation Date: Tuesday, September 26, 2017
Start Time: 9:45 AM
Location: Exhibit Hall C/D
Presentation Type: POSTER
San Andres formation is a dolomitized carbonate and an oil-and gas-bearing member of the Upper Permian in the Permian Basin. It has been produced with vertical wells that were either waterflooded or CO2 injected for primary, secondary, and tertiary recovery. Some of the early waterfloods date back to the 1960s. Historically, the San Andres formation is associated with high water cuts. This paper proposes an integrated solution from planning to completion of a horizontal well, with an aim to control water production. The workflow involves the integration of various technologies such as crosswell seismic, petrophysical logs, geomechanical logs, fracture modeling, and real-time microseismic monitoring.
Stratigraphic surfaces were created using the crosswell seismic data tied in with well tops from offset vertical wells. The 3D model was populated with high-tier petrophysical and geomechanical properties from the pilot well. The zones with high water saturations were identified in the subsurface, which gave an insight into the source of the produced water. Fully 3D planar fracture modeling was performed using the log data from the vertical offset well at the landing point of the horizontal well. Sensitivities were performed on various fluid systems, job volumes, and pump rates, and a playbook was created for real-time operations as part of a contingency plan.
Lateral measurements included petrophysical and geomechanical data, which were used to place perforations, within a stage, in similar type of rock. Depending on the real-time microseismic events, the stimulation design was changed on the fly. Stages with events that were growing out of the zone were modified first, and a final pump schedule was established after the first five stages.
The production results indicated a 20% decrease in water cut, which is a notable improvement compared to the historical production data in the San Andres. The workflow proved that the water production can be significantly reduced by applying a methodology that includes integration of data from multiple domains, thereby improving the economics of a well.
To investigate the effect of vesicular property on mechanical characteristics of basalts a series of uniaxial and triaxial compression tests were conducted for basaltic intact rocks sampled in the northeastern onshore and offshore, southeastern offshore and northwestern offshore of Jeju Island, South Korea. The uniaxial compressive strength and parameters used in the More-Coulomb failure criterion, namely cohesion and internal friction angle, estimated from the results of the uniaxial and triaxial compression tests were compared and analyzed with effective porosity, a parameter representing the vesicular property of basalts. The results demonstrate that the uniaxial compressive strength and cohesion with respect to the effective porosity can be classified clearly as two different non-linear regression curves in accordance with two different linear relationships between bulk specific gravity and effective porosity. As the effective porosity increases, the uniaxial compressive strength and cohesion decrease exponentially. On the other hand, the internal friction angle decreases gradually with the effective porosity, regardless of the relationships between bulk specific gravity and effective porosity.
Basalt is one of the most common rock types of volcanic lava area, and has a fine-grained mineral texture. In addition, basalt has various shaped and sized vesicles formed by dissipation of gaseous phases in lava decompressed in the process of erupting onto the surface of the earth or flowing on the surface.
Vesicular structures of basalt have important effects on the physical and mechanical properties of the intact rock itself as well as the stability of rock mass which are crucial for the design of diverse foundation structures, tunnels, and other projects.
There are many studies of the effects of vesicular property on the physical and mechanical properties such as permeability, uniaxial compressive strength, elastic modulus, Poisson's ratio and ultrasonic velocities of vesicular basaltic intact rocks (Kelsall et al., 1986; Kim and Choi, 1991; Kwon et al., 1993; Al-Harthi et al., 1999; Saar and Manga, 1999; Eum, 2002; Kim, 2006; Gates, 2008; Cho et al., 2009; Moon et al., 2014; Yang, 2014; Yang, 2015a; Yang, 2015b; Yang, 2016; Yang and Sassa, 2016). Most studies on the basaltic intact rock revealed the relationship between physical parameters representing vesicular property and mechanical characteristics estimated from the results of uniaxial compression test. There are, however, very few studies about the strength parameters, such as cohesion and internal friction angle, which can be estimated directly from the results of three or more triaxial compression tests on basaltic intact rocks.
Three measurement campaigns were carried out by Natural Resources Canada CANMET Laboratories over the last thirty years within the Red Lake Gold District, Ontario, to determine the magnitude and orientation of in-situ rock stresses on several levels of the Campbell and Red Lake gold mines, at depths ranging from 600 meters down to 2,000 meters below surface. Stress measurements were carried out using standard CSIR triaxial 'hollow-inclusion' and biaxial 'doorstopper-type' measurement cells. In-situ 3D stress tensors were computed. Increasing with the depth of measurement, the major principal stress varies between 23 and 95 MPa, the intermediate stress, between 14 and 68 MPa, and the minor principal stress, between 4 and 38 MPa. The measured vertical stress component also correlates well with the stress level expected within the Canadian Shield at these depths, ranging from 16 MPa at 580 m below surface up to 54 MPa at a depth of 2,000 m. The average stress ratios measured between the principal and vertical stress components are 1.62, 1.01 and 0.55, respectively, confirming the presence of a strong and consistent shear-stress tensor arrangement for all tensors measured below 650 m. This stress arrangement perfectly fits the geological strain-model proposed by Dubé et al. (2002), to explain the formation and the resulting geometry of the Campbell-Red Lake gold deposit, its evolution over time and the development of high grade mineralization zones at depth. The model was namely validated by the latest stress measurement campaign carried out on the deepest levels of the Red Lake Gold Mine during winter 2011. These measurements are key to understand the influence of such high shear stresses on mine design and excavation stability. Sources of variation, e.g. number and complexity of rock layers, presence of faults and folds, dykes and other major geological features, are discussed. ©Copyright reserved, Natural Resources Canada.
The Middle-Triassic Gulailah Formation, also known as the Jilh Formation, was poorly understood in Abu Dhabi due to lack of data integration. A recent study involving mapping of the internal architecture of the formation on the basis of regional seismic data and all available wells across Abu Dhabi shows the evolution of an intra-shelf basin during deposition of the Gulailah Formation which was overlooked during previous studies.
Interpretation of regional mud logs and updated isopach maps show a deepening trend from a shallow shelf in the northwestern offshore Abu Dhabi to a depo-center in the southern onshore. The isopach contours imply an increase in water-depth toward the basin center and mark the outline of the Gulailah intra-shelf basin as a restricted depression on the Middle-Triassic to Middle-Jurassic shallow-water carbonate shelf. The basin margin is characterized by a shallow-water shelf break, where the sudden change in slope leads to a higher thickness gradient. The regional variation of seismic reflection patterns from prograding and thickening events around the shelf-break to parallel reflections at the depo-center characterize the general geometry of the Gulailah intra-shelf basin from basin margin to basin center. Detailed well correlations based on GR cycles corresponding to 3rd-/4th-order sequences show a layer-cake model at the bottom followed by a prograding sequence towards the top of the Gulailah, representing the evolution from a gentle ramp to an intra-shelf basin.
In the Lower Gulailah, laminated algae-related dolo-mudstone with desiccation cracks and intercalated anhydrite layers indicate a low-energy tidal flat environment in the northwest. The increase of sub-tidal lime-mudstone to the east and to the south indicates a deepening of the carbonate ramp system in those directions. Influenced by the Late-Triassic uplift of the Qatar Arch, the Upper Gulailah subsequently developed into an intra-shelf basin with a more confined accommodation space, where carbonate sediments gradually filled-up the basin as low-angle prograding ramps from the northwestern offshore to the southern onshore. At the base of the Upper Gulailah, low-GR grainy facies extend from the basin margin to the basin center, indicating a shoal-related depositional setting. Above this interval, prograding ramps are dominated by muddy facies, indicating a more restricted environment. Micro-conglomerates and breccia intercalated with thin layers of grainy shoal sediments reflect a peritidal dominated environment between the shelf-break and the basin center. Tight limestones with thin beds of shale representing a deep sub-tidal environment were deposited in the basin center.
Different from the well-known reef-originated Bab basin, the Gulailah intra-shelf basin is a consequence of tectonic activities. High-relief reefs are not developed due to highly-frequent clastic influxes and high salinity. The basin is characterized by low-angle prograding ramps, thickening towards the basin center, and gradually filling-up the shallow basin during a period of relatively stable sea-level.
In recent years, numerical reservoir simulation (3-dimensional modelling) has become a very useful optimisation tool, not just for field development planning but also for ongoing reservoir management. Although several analytical methods (such as material balance equations, Buckley-Leverett displacement theory etc) are used as computationally fast and inexpensive tools, they have been recognised as being incapable of capturing the details and complexity of certain reservoirs and processes.
The field presented in this paper is one of the biggest oil fields in the Niger Delta, with an estimated oil in place of over 2.5 billion barrels and cumulative oil production close to 1 billion barrels. About half of this volume and production come from a single reservoir, which is densely faulted. The large number of intra-reservoir faults and the relatively high offtake rates have inhibited the activity of the otherwise strong aquifer and resulted in the high pressure decline observed in this reservoir. Consequently, a lot of the wells quit at relatively low water cuts of 40-50%, with the reservoir pressure being insufficient to lift the crude to surface at higher water cuts.
One of the recommendations of the FDP Update was to increase oil recovery through fieldwide installation of gaslift. However, to quantify the gains of gaslifting and optimize oil recovery through effective reservoir management, an integrated detailed 3D model was required due to the structural complexity of the reservoir. This paper presents the workflow used in constructing, initializing and history-matching the 3D reservoir model; and how the history-matched model was used to assess different development scenarios for improving recovery from this large mature reservoir.
The Eastern Barents, Kara, Laptev, East Siberian seas and the western Chukchi Sea occupy a large part of the Eurasian shelf in the Russian Arctic. This huge region consists over 40 sedimentary basins of variable age and genesis, which are thought to bear significant undiscovered hydrocarbon resources. Apart of the East Barents and South Kara shelves with proven world-class gas and gas condensate resources, the rest of the basins are undrilled and explored with rather sparse grid of regional 2D seismic lines.
The majority of the sedimentary basins were formed and developed in a rift and post-rift setting and later modified through a series of structural inversions. Important tectonic events controlling the structure and petroleum geology of the basins are: the Caledonian collision and orogeny followed by Late Devonian to Early Carboniferous rifting, Late Paleozoic Baltica/Siberia collision and Uralian orogeny, Triassic and Early Jurassic rifting, Late Jurassic to Early Cretaceous Canada Basin opening accompanied by closure of the Anyui Ocean, the Late Mesozoic Verkhoyansk-Brookian orogeny, and Cenozoic opening of the Eurasia Oceanic Basin.
Using available regional seismic lines correlated with borehole data, onshore geology in areas with no exploration drilling, and the Arctic-wide magnetic, bathymetry and gravity grids, we provide more confident characterization of the regional structural elements of the Russian Arctic shelf, and constrain the timing of basin formation, structural styles, lithostratigraphy and possible petroleum systems and plays in frontier areas.