Saudi Arabia has embarked on an exploration journey for its unconventional gas resources by recently targeting three different areas across the Kingdom. The targeted formations include tight sandstone, shale and tight carbonate with a permeability range of 200 nano-darcy to 0.1 MD. Extensive exploratory work has been performed in each of the areas through drilling vertical wells to identify and characterize potential targets through coring and open-hole logging along with flow potential testing of those targets after placing vertical fractures, which is beyond the scope of this paper. This paper highlights the progress of the unconventional program through drilling horizontal mono-bore wells and stimulating them with multistage fracturing using Plug-N-Perf technique. Three case studies, one from each targeted formations, are presented in this paper. The subjects addressed are: Well completion including the selection of tubing and liner sizes, metallurgy and grades along with performing stress and thermal analysis simulating the expected loads during proppant fracturing to determine the maximum safe loads at each stage. Proppant fracturing design including the number of stages and clusters, the spacing of stages, proppant type, size and volume, and fracturing fluid systems. The design is based upon the geomechanical and petrophysical interpretations of the openhole logs together with onsite calibrations and measurements. Plug-N-Perf and fracture stimulation operations and execution Fracture fluid clean up and flow testing The paper summarizes the workflow adopted, the lessons learned and challenges overcome after drilling, completing, fracturing and flow testing of several unconventional gas wells in Saudi Arabia.
One of main challenges operators face in evaluating the potential of unconventional reservoirs is the complex geologic nature of organic rich, fractured, laminated, and heterogeneous formations having implications on stimulation and production optimization. An area with a limited number of stimulated appraisal wells in the Jurassic mud rocks in Saudi Arabia was targeted for this study. The objective is to build and calibrate a multidisciplinary integrated workflow consisting of geologic, hydraulic fracture, and reservoir modeling to optimize the number of clusters and other completion parameters for a multi-well pad drilled in the subject area. The workflow developed comprises integration of data analysis to evaluate reservoir and completion qualities and assess their impacts on production performance specifically for unconventional reservoirs. Petrophysical and geomechanical models were calibrated with core measurements. Logs from the horizontal lateral was integrated in the geomechanical model to analyze the hydraulic fracture stimulation by performing fracture pressure matching for all stages. The hydraulic fracture attributes from the fracture simulator were exported to the reservoir simulator. The surface production measurement together with the production log were used to calibrate the reservoir model. The final calibrated workflow, including hydraulic fracture and reservoir models, was used to perform sensitivity analyses to optimize the cluster spacing and other completion parameters considering the geomechanical and reservoir constraints. Preliminary results suggest stress shadowing is not a major concern even with a short cluster spacing given the level of stress anisotropy in this formation. An optimum cluster spacing was determined based on long-term production performance. The results of this study were implemented in a pilot well pad to determine which completion variables were critical for optimizing well productivity and further calibration of the workflow. The methodology adopted in this study identifies the major controlling factors of completion and reservoir parameters affecting well productivity for specific unconventional reservoirs. This workflow will help shorten the learning curve and increase the efficiency to reach the optimum stimulation design for the development phase.
Gaining an understanding of the well to well interference during hydraulic fracturing and subsequently production interference is paramount in optimizing the costs associated with field development. Much work has been done in the industry to better understand the interference during hydraulic fracturing and production among adjacent wells. This paper presents an analysis that employed both a pressure interference analysis and chemical tracer analysis to gain a better understanding of the fracture interference in a well pad in the Jafurah field. The subject pad consists of 4 wells. Two of which run parallel in a north direction and the other two run parallel in the southern direction. All four wells were hydraulically fractured with slickwater design. Adjacent to the subject pad is another pad that had been previously stimulated with crosslink design and was used for pressure monitoring. The distance between the laterals was relatively similar (X ft) with one exception (2 × ft). Initially, one well from both directions was stimulated with 33 stages each of slickwater design and the plugs were subsequently milled out. Afterwards, the other two wells were stimulated with 33 stages of slickwater each. In 7 of the 33 stages of the later wells, 20 oil and 20 water tracers were injected in sequence in an attempt to study the physical extent of the fractures generated. While the latter two wells were being stimulated, the wellhead pressure on the parallel wells was being monitored and recorded along with the wellhead pressures on the adjacent pad. During flowback, the southern wells were flowed back simultaneously and flowback samples were collected to be analyzed for tracers. Subsequently, the northern wells were opened up to flowback in the same manner and flowback samples were also collected for tracer analysis. Wellhead pressure was monitored on the adjacent pad during flowback of all the wells. The pressure data during the fracturing operation indicated for distance × ft and the size of stimulation stages pumped, a level of communication which was further verified by the production interference analysis as well as the tracer data.
Saudi Arabia has embarked on an exploration journey for its unconventional gas resources by recently targeting three different areas across the Kingdom. The targeted formations include tight sandstone, shale and tight carbonate with a permeability range of 200 nano-darcy to 0.1 MD. Extensive exploratory work has been performed in each of the areas through drilling vertical wells to identify and characterize potential targets through coring and open-hole logging along with flow potential testing of those targets after placing vertical fractures, which is beyond the scope of this paper. This paper highlights the progress of the unconventional program through drilling horizontal mono-bore wells and stimulating them with multistage fracturing using Plug-N-Perf technique. Three case studies, one from each targeted formations, are presented in this paper. The subjects addressed are:• Well completion including the selection of tubing and liner sizes, metallurgy and grades along with performing stress and thermal analysis simulating the expected loads during proppant fracturing to determine the maximum safe loads at each stage. • Proppant fracturing design including the number of stages and clusters, the spacing of stages, proppant type, size and volume, and fracturing fluid systems. The design is based upon the geomechanical and petrophysical interpretations of the openhole logs together with onsite calibrations and measurements. • Plug-N-Perf and fracture stimulation operations and execution • Fracture fluid clean up and flow testingThe paper summarizes the workflow adopted, the lessons learned and challenges overcome after drilling, completing, fracturing and flow testing of several unconventional gas wells in Saudi Arabia.
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