Objectives/Scope Rock fabric characteristics of Gamij Field lies in the purview of conventional reservoirs but are as complex and uncertain as unconventional. It is a multi-layered, heterogeneous reservoir on depletion drive with very low permeability. Even after hydraulic fracturing and artificial lift, the production rate lies in the range of 3-4 m3/d. This paper evaluates the impact of past hydraulic fracture operations and uses this understanding to optimize the stimulation strategy for future wells. Methods, Procedures, Process A customized multidisciplinary modeling and flow simulation workflow; integrating petrophysical, geomechanical, stimulation and production data was adopted and applied to sectors of the field. Two techniques were combined 1. Unconventional (Fast Loop) 2. Conventional (Slow Loop) in an intriguing and iterative manner. Hydraulic Fractures were designed, optimized and calibrated using a rigorous workflow of unstructured grid and unconventional fracture modelling/3D planar fractures in the sector models. Sector model is considered the most effective approach to characterize completion quality in Gamij Field due to the limitation of current modelling technologies to design and simulate hydraulic fractures in full-field model. Results, Observations, Conclusions The results of sector model is validated with full field model and a number of iterations were performed to match pressure from the result to the initially assumed in creation of 3D MEM (Mechanical Earth Model). Reservoir quality (RQ) estimation is affected by complex mineralogy including abundance of iron and titanium rich sediments. Stress regime shows vertical transverse isotropy nature of shales and suggest re-orientations near to fault zones. There are several areas, especially in the eastern part, where the tectonic regime changes from normal to strike-slip faulting. HF modelling not only explains the contrasting behavior of existing wells, but also discusses alternatives that could help to unlock the true potential of the pay zones. This paper elucidates techniques to maximize reservoir understanding and allow optimization of hydraulic fracture design in terms of casing diameter, job size, and design. Simulations shows multiple fractures were created from different preformation cluster in a single stage treatment. Overall, the case study showcases different factors that govern the development of a tight oil reservoir and the ways to characterize and quantify these uncertainties. Novel/Additive Information This work is the first step to quantify the complex reservoir mineralogy, impact of laminations, depletion, stress variation on the efficiency of HF jobs. Identification of potential sweet spots based on reservoir quality and completion quality indexes, establishing well productivity. The uncertainty cannot be eliminated but it ought to be reduced and risk analyzed before the actual execution.
Field G in Upper Assam, India is a highly faulted basin, under decline phase since its first production in 1974. The region is characterized by heterogeneous distribution of in-situ stress, depleted pressure gradient (0.25psi/ft) and low permeability (<1mD). Previous conventional fracturing attempts in the area were unsatisfactory. This paper describes the lifecycle of production enhancement project carried-out in this field starting from fit-for-purpose candidate selection methodology to implementation and success of infinite conductivity channel fracturing. Reducing pressure drop within fracture and enhancing fracture effectiveness is fundamental to take the production to next level in this field. Meticulous well-centric-study approach was implemented to rank 5 best candidate wells (including injectors) from plethora of wells lying in tectonically complex field. Formation petro-physical properties and off-set wells data was interpreted to synthesize mechanical-earth-model for selected wells. Detailed geo-mechanical formation evaluation using various Injection tests and Planar-3D model were applied to decide correct well completion and fracturing technique. Best practices were developed to overcome inherent challenges of this region involving deep, tight sands with mid-field tortuosity and high-pressure operations. This study specifies the results of over 15 injection tests (Step Rate tests, Re opening tests, Calibration injection tests) carried out in the field and how the injection test methodology was customized from well to well, catering to specific challenges from each well. By understanding the unique pressure decline response from the formations, insight was gained into rock deformation that generated particular stress field during the geologic past. The fluid leak-off response, rock mechanical properties and net pressure development in Calibration injection were used to estimate the final fracture geometry. An all-inclusive approach for well completions and the use of channel fracturing instead of conventional fracturing techniques have reduced the screen-out risk, ensured successful fracture placement and increased production up to 100% increment in oil. The Oligocene-Eocene aged reservoir facies, marred by various strike/slip faults has developed an uneven stress regime in this field that makes fracturing treatments very challenging. The paper covers a comprehensive research on the analysis of first-ever-application of channel fracturing in Assam basin. This study incorporates a novel practical guide to address issues of multiple complexities occurring simultaneously in a reservoir like presence of tectonic stress, fracture misalignment and high tortuosity.
Hydraulic fracturing can establish well productivity in tight and unconventional reservoirs, accelerate production in low- to-medium permeability wells and revamp production in mature wells. However, not all wells are suitable candidates for hydraulic fracturing and the technique can be detrimental if the right candidate is not chosen. An integrated approach is required to select the wells that are the most-suitable candidates for hydraulic fracturing. This paper discusses the hydraulic fracturing candidate selection workflow and execution carried out in the year 2015 to 2016, which has unlocked reservoir production potential of Upper Assam basin fields of Oil India Ltd. (OIL). Wells which showed poor/no inflow prior to hydraulic fracturing operations, exceeded operator expectations during post fracturing production. Better reservoir management through hydraulic fracturing, rejuvenated ceased wells with an incremental oil production rates of 1380 bopd cumulative rate from six wells, post fracturing. The candidate analysis workflow described in this paper, can serve as the best practices guide for any operator investigating workover candidates among multiple fields, with an objective of production enhancement. A customized candidate selection methodology was developed to identify the 10 best candidates from a pool of 70 vertical/deviated wells in two phases of the hydraulic fracturing campaign. In the absence of dynamic reservoir analysis, offset well data analysis assisted in filling the data gaps by enabling geological and reservoir level understanding. Well production models were calibrated with the production history, geo-mechanical models were prepared and used in the fracture modelling to generate optimum fracture geometry and predict post-fracturing production. Wells were ranked according to incremental hydrocarbon production coupled with risk factors including completions integrity. In the execution, fracturing model was validated by performing fracturing diagnostics tests such as Step Rate and Minifrac injection. The final calibrated model was then used to design the optimum fracturing treatment. Given the age of wells and traditional completions architecture, best practices were developed to counter challenges of high pressures and rate limitations in wells with depth greater than 3500 m. As stimulations and well preparation in completed wells are expensive, it was critical to identify the most-suitable candidates with the available dataset before attempting well preparation and further acquisition. This was addressed through a customized workflow to perform production rate transient analysis for reservoir dynamic flow properties, create synthetic geomechanical models for stress profile & fracture vertical growth estimation.
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