TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractA minifrac test is usually performed before a fracture stimulation treatment to calculate formation and fracture properties. Recently the analysis techniques were extended to the after-closure period. The after-closure data are analyzed to calculate formation permeability and reservoir pressure.Technology developers have hypothesized the existence of either pseudo-radial or linear flow behavior during the afterclosure region. Identifying the presence of the flowing regime is an awkward process at best. The roots of the linear flow equations are different from those of the pseudo-radial flow equations. Many tests do not follow either flow regime.In this paper, we have created a general approach for analysis of after-closure pressure decline data. Because the determination of the flow regime and type of fracture depends only on time and monitored pressure, the analysis may even be performed in real time. The technique determines whether sufficient data have been obtained to perform a reliable analysis. The calculated parameters would be used to update the fracture design and, in turn, for performing the fracture treatment.The new technique is simpler and more generalized than what currently exists. The technique initially determines whether analyzable data exist. It shows that three flow regimes may dominate the after-closure region, depending on the reservoir properties and residual fracture conductivity. The technique presented not only determines the type of regime, and consequently, the type of residual fracture, it also determines the formation permeability and reservoir pressure.There is no reason to restrict the application of this test to minifrac test analysis. We believe the approach is also applicable to analysis of data after performing a fracture stimulation treatment. A numerical simulator was used to model the pumping and closure process and to validate the new approach.The paper also presents a detailed discussion and analysis of several field cases, demonstrating the various flow regimes and, ultimately, the validity of the developed technique.
Influenced by the success of shale gas production worldwide and to meet requirements for clean energy supply, a multidisciplinary team of petroleum specialists was established in Saudi Aramco. Meeting the growing requirement in industrial consumption and especially electricity production is a driving force for developing unconventional gas reserves. "The initial focus is in the northwest and in the area of Ghawar, where gas infrastructure exists. Initial knowledge building from similar plays in North America is being supplemented with internal technical studies and research programs to help solve geological and engineering challenges unique to Saudi Arabia and to locate specific wells planned for 2011. The company is innovatively combining knowledge and research to maximize gas reserves and production from conventional and unconventional resources in order to meet growing domestic demand" (1). During years 2010 -2011 major international petroleum industry players -Schlumberger, Halliburton and Baker Hughes -were invited to share their experience in a series of workshops held in Dhahran. Exchange of expert ideas developed into appreciation of complexity of the shale gas reservoir and helped to identify the scope of work for the first Silurian Qusaiba shale gas well. The SHALE-1 well was drilled in 2007 as a gas exploration well. Recent drilling and geophysical data obtained in the well were beneficial for detailed sidetrack and fracture stimulation design. The Multidisciplinary Saudi Aramco -Halliburton SHALE-1 task group was established and positioned in Dhahran. This allowed them to have regular face-to-face meetings and improve the most critical criteria of any new venture -communication. The draft work plan was developed 8 months before actual operations commenced on the well site. Thorough examination of the draft work plan progressed to the final work plan with a number of improvements. For example, "R" Nipples were dropped from the monobore 4-1/2" completion string. The Frac Stimulation design was fine-tuned, involving expertise from Saudi Aramco and Halliburton. The Complete Well on Paper exercise involved over 25 specialists from both companies and helped to rectify remaining completion/stimulation design issues, and put everyone on the same page in terms of the work program. Well site operations commenced in May 2011; the well was successfully re-entered and window cut in 7" liner. An S-shaped 5-7/8" hole was drilled in the direction of minimum horizontal stresses, to the required depth in Qusaiba Shale with a maximum DLS of 4°. The well was completed with a 4-1/2" cemented liner and monobore 4-1/2" string to surface. The Hot Qusaiba interval was perforated, frac stimulated with mixed results, and successfully flowed. A temporary isolation ceramic (easily drilled) plug was set above the perforation interval. The Warm Qusaiba interval was perforated, successfully frac stimulated, and flowed with mixed results. Finally, the plug was drilled out with CTU and both intervals flowed and required production log...
SPE Members Abstract This paper describes the laboratory and field work performed to understand and improve the stimulation of the fractured carbonate formation producing in the Lisburne Field, Prudhoe Bay, Alaska. Within the producing formations, the lower Wahoo intervals are low permeability, fractured dolomitic zones that produce poorly when compared to the higher permeability upper intervals. Past attempts to stimulate these intervals have included propped fracture techniques and standard acid fracture techniques. A laboratory study evaluated the effects that various acid systems have on Wahoo rock properties, the degree of permeability enhancement, and stability of acid fracture conductivity. Various acid fracturing techniques were also investigated to determine which technique and acid system created long-term fracture conductivity. The laboratory study indicated the optimal treatment would be obtained by using emulsified acid in a fracture acidizing treatment followed by a closed fracture acidizing stage using emulsified acid. The unique combination of this particular acidizing technique and acid system has increased productivity in the Lisburne Field. Complete documentation of the field work optimization program is included in this paper. Pressure buildup (PBU) analysis has indicated fracture half lengths are from 25–100 feet long and production spinner surveys have determined that lower intervals are contributing to production. To date, over 40 new and old wells have been stimulated using emulsified acid with the closed fracture acidizing technique. Significant increases in production and reserves are currently being seen from this program. Introduction Initial well stimulations in the Lisburne field consisted of 1/2 bbl/foot, approximately 100 bbls of 15% hydrochloric acid (HCl) pumped at matrix rates. Because of high perforation density, diversion was difficult with ball sealers or particulates. Production responses after these treatments were good with initial rate increases of 2,500–3,000 bopd, but rates declined rapidly during the first month of production. Production surveys indicated that the majority of production was coming from the top 10–20 feet, identified as a subunconformity alteration zone, or 'SAZ'. This interval is a highly permeable zone that is believed to be locally interconnected with the rest of the reservoir through faults and fractures. As development continued, less prolific wells were drilled as a result of poorer quality reservoir rock and because of 'SAZ' depletion. This situation required the development of a new stimulation technique to enhance production from the lower permeability intervals. Some early attempts to increase the productivity of these lower zones were acid fracturing with alternating stages of gelled water and 28% HCl and propped hydraulic fracturing. The initial acidfracs resulted in high initial rates but production rates declined rapidly to pre-stimulation rates. Simple acid fracturing created etched fractures that were too short. Deeper acid penetration was required to sustain long term productivity. Propped hydraulic fracturing limitations included conditions such as, low pump rates through 2–7/8 inch production tubing, high shot density in all intervals, and large gross thicknesses. P. 923^
When a well is hydraulically fractured, the propagation of the fracture away from the wellbore is dictated by the far field stresses in the reservoir. However, the fracture initiation from the wellbore depends strongly on the near wellbore stress state created by drilling the well. Misaligned fracture initiation and propagation planes can reduce the wellbore-to-reservoir connectivity causing operation failure and high post fracturing skin.Currently creating multiple fractures along a horizontal openhole requires mechanical isolation means such as openhole packers or sand plugs. They can be costly and time consuming. In addition, there is no control of fracture initiation within one isolated section. Undesirable competing fractures within the zone can occur to impact the fracture length. Significant improvement can be made if the factors controlling multiple fracture initiation without mechanical isolation can be understood.Experimental work in multiple fracture initiation has been rare, controlled multiple fracture initiation is non-existent. Therefore a series of laboratory experiments was performed in a true tri-axial stress frame to investigate how multiple fractures can be initiated in a controllable fashion. In the tests, notches at specific locations along the openhole wellbore were created. The impact of the notch depth on the orientation of the hydraulically induced fractures was studied.In addition to the experiments, continuum fracture mechanics modeling using finite element was also conducted to rationalize the experimental observations of fracturing initiation process in the rock.The results of block tests provided new insight in multiple fracture initiation. By monitoring the real time acoustic emission events, the sequence of fracture creation as wellbore pressure increased was visualized. The finite element modeling gives simple criteria to explain the observed orientation of initiated fracture as a function of notch depth. IntroductionThe productivity of horizontal wells may be enhanced by inducing multiple hydraulic fractures along the wellbore. The propagation of a fracture away from the wellbore eventually is determined by the far field stresses in the reservoir. Assuming isotropic homogeneous formation properties, a longitudinal fracture will propagate along the axis of the horizontal wellbore when the well is drilled into the maximum principal horizontal stress (σ H ). A transverse fracture will propagate if the well is drilled into the minimum principal horizontal stress (σ h ). However, the fracture initiation from the wellbore is more complex (Daneshy 2009). It depends not only on the reservoir stresses orientation, but also is influenced by the near wellbore local stress state due to the drilling of the well. The mechanical properties of the rock, the surface condition of the wellbore wall, the rate of pressurization, and the physical properties of the fracturing fluid also play important roles in fracture initiation direction. Fracture initiation, though does not necessarily alter the fa...
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