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Collaborating Authors
Well & Reservoir Surveillance and Monitoring
Abstract Tight-gas, low-permeability reservoirs offer a tremendous challenge with respect to effectively completing and draining a target reservoir. Openhole-packer completions in horizontal wells offer a cost-efficient means of accessing the entire lateral section, assuming the target pay can be effectively stimulated. The challenge with openhole completions compared to more conventional cased, cemented, and limited-entry perforated completions is understanding and controlling hydraulic-fracture geometry; specifically, the number and location of fracture-initiation points and the fracturing-fluid flow into the near- wellbore (NWB) area of the reservoir. Fiber-optic-based distributed temperature sensing (DTS) offers a method for identifying, quantifying, and evaluating the NWB fracture geometry, the fracturing-fluid distribution in these broad openhole sections, and overall stimulation effectiveness. DTS can also reveal success or issues with respect to effective zonal isolation when using mechanical isolation during the hydraulic-fracturing process. In this particular case study, a lateral well in a basin-centered gas (BCG) area was completed with swell-packer interval isolation using fracture sleeves for reservoir access. By coupling fracture-treatment responses and openhole log characteristics with the NWB DTS data during pumping and warm-back, an integrated assessment of the completion stimulation effectiveness and efficiency was performed. The end result of this assessment provided an improved understanding of the current completion performance and allowed optimization of openhole completion projects for future wells in this same area.
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Mudrock (0.31)
Abstract In this paper, the sensitivity of expected ultimate recovery (EUR) for horizontal wells with multiple fractures to decline exponent is studied using the simplified forecasting method introduced by Nobakht et al. (2010). This is very important from the reserves evaluation perspective due to uncertainty in decline exponent, b. This uncertainty is caused by many factors like adsorption and reservoir/completion heterogeneity. It is found that in case of time-based forecast (duration of forecast is specified), the ratio of EURs for two different specified values of decline exponent depends on the ratio of economic life time of a well to the duration of linear flow. On the other hand, this EUR ratio depends on the ratio of rate at the end of linear flow to economic rate limit for economic limit-based forecast (economic rate limit rate is specified).
- North America > Canada > Alberta (0.29)
- North America > United States > Colorado (0.29)
- North America > United States > Texas (0.29)
- North America > United States > Texas > Fort Worth Basin > Barnett Shale Formation (0.99)
- North America > United States > Colorado > Piceance Basin > Williams Fork Formation (0.99)
Abstract The appraisal of deep tight gas reservoirs can be technically and economically challenging, with success dependent on applying the most efficient completion technology. Inevitably, this includes designing well completions that encompass the deployment of multiple hydraulic fracturing treatments. There is a tendency in the completion design phase to under-assess the number and variety of interventions that a well could undergo during its evaluation. Subsequently, the development and application of the appropriate well intervention strategy is crucial in maximizing the well potential and reservoir understanding. The deliverable of any tight gas appraisal program is to increase the level of confidence in continuing to pursue the resource opportunity by demonstrating stable and sustainable gas inflow flow rates. Recent drilling success targeting deep frontier gas reservoirs, such as the Amin located in the central part of Oman, have resulted in the need to evolve the well intervention process to include several new (for the region) technologies. These included the deployment of abrasive perforating to facilitate the initial formation breakdown operations, milling out the shoe track for a hydraulic fracturing treatment in an openhole setting, restoring full wellbore access by milling out multiple frac plugs, and temporary installation of a velocity string to eliminate liquid loading issues. Historically, many of these individual processes have been attempted or deployed with varying levels of success, but this is the first time that they have been integrated into a well strategy. This paper summarizes the process of selecting the best options for well intervention operations in low-permeability gas reservoirs. The integrated work design consideration and results of these completion techniques will be presented along with the key learnings derived from the process.
- North America > United States > Texas (0.47)
- Asia > Middle East > Oman (0.36)
Optimizing Borehole Imaging for Tight Gas Exploration: Evolving a Go-No-Go Decision Tree in Tight Gas Reservoirs of the Sultanate of Oman
Shrivastva, Chandramani (Schlumberger) | Al-Mahrooqi, Sultan (Petroleum Development Oman) | Mjeni, Rifaat (Petroleum Development Oman) | Kindy, Suleiman (Petroleum Development Oman) | Hosein, Feraz (Schlumberger Oman) | Al-Busaidi, Hafidh (Schlumberger Oman) | Al-Busaidi, Jokha (Schlumberger Oman) | Laronga, Robert (Schlumberger)
Abstract Borehole images play a crucial role in tight gas exploration. Recognition of sedimentary features helps in understanding the depositional architecture and allows refinement of the facies model for flow unit identification and stimulation treatment. The structural analysis of faults and fractures provides clues not only about the tectonic history, but also about the possible conduits for fluid migration that lead to diagenesis. The diagenetic imprints and their impact in a sequence stratigraphic framework can be understood through textural analysis performed on the borehole images across the field. And, hydro- fracturing of tight gas reservoirs require important input from the borehole images in understanding the variability of stress regimes. Established micro-resistivity imagers for the water-base mud (WBM) environment provide robust results, except when there is a large contrast between the formation resistivity (Rt) and the mud resistivity (Rm). With more frequent use of hyper-saline mud, a new and improved definition imager is deployed to obtain high quality images. Novel hardware and improved signal processing algorithms are employed to acquire the images despite the hostile conditions provided by the combination of low- resistivity salt-saturated (WBM) and high formation resistivity that would otherwise impede the data quality. Early field testing of this enhanced capability took place in the Sultanate of Oman and the examples of its improved performance are presented. Getting the most detailed image data in oil-base mud (OBM) is challenging compared to the WBM systems. As an alternative to the options commercially available in the industry today, the new high-definition imager developed for the WBM system can also be used under favorable conditions to acquire valid images in the OBM. The high-definition imager works best in OBM when both formation resistivity and mud permittivity are high. A workflow is developed for the Go – No Go decisions for borehole imaging tools in different mud systems for tight gas reservoirs. It is important at the planning phase of the logging programs to anticipate the imaging tool behavior in the proposed mud system and conditions. The results from trials made in the tight gas reservoirs of North Oman provided the basis for a decision tree for imaging, since the logging environment exerts a strong control on data quality. The decision-tree presented here aims to ensure that images acquired are the most suitable for detailed geologic interpretation and subsequent integration in development plans for optimal exploitation of tight gas sands in Oman.
- Geology > Sedimentary Geology (1.00)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Sandstone (0.95)
- Geophysics > Seismic Surveying > Borehole Seismic Surveying (1.00)
- Geophysics > Borehole Geophysics (1.00)
- Reservoir Description and Dynamics > Unconventional and Complex Reservoirs > Tight gas (1.00)
- Production and Well Operations > Well & Reservoir Surveillance and Monitoring > Borehole imaging and wellbore seismic (1.00)