For the past few years ADNOC has extensively ramped up its effort in exploring and testing unconventional reservoir across Abu Dhabi tight oil and shale gas formation as part of its oil & gas 2030 strategy. Shilaif tight oil exploration started over 5 years ago with multiple vertical wells drilled and tested allowing discovery of stacked tight oil play with significant resources in place. To unlock these resources, horizontal drilling and multistage fracturing were used to confirm recoverable resources, and well potential. Prolific production results have since propelled hydraulic fracturing, hence it has become imperative to build a process to standardize unconventional fracturing technical and operational requirements and to maximize efficiency and benefit. A prime example of such process was in Huwaila-68 where the organic-rich Shilaif shale/tight oil formation was targeted. A target that is analogous to the Eagle Ford from the same Late Cretaceous age. A significant weight is put on reservoir quality assessment to minimize margin of error and increase the probability of fracturing success, and to maximize recovery of the estimated tight oil and shale gas in place. This process assessed the Shilaif from a geological, petrophysical, and geomechanical perspectives. This was followed by setting up preferential staging and perforation placement strategy for fracturing based on reservoir and completion quality which correlated to an initially built 1D mechanical earth model. Production forecasting using reservoir simulations were also utilized to assess fracturing success and deliverability. The processes above led to completing multistage fracturing in Huwaila-68 within the Shilaif formation by means of a pump- down perf and plug operation coupled with high rate slick water pumping, which was followed by extensive well testing. Operational efficiency allowed for the completion of 27 stages placing in excess of 7.3 million lbs of proppant. The use of chemical tracers as a qualitative measure allowed for correlation between natural fracture presence, recorded pumping events, and initially recorded gas shows while drilling. Such observations would help in well placement for future horizontal wells. Post fracturing production rates have met expectations, and were in line with the initial reservoir assessment predictions. The novelty of this paper is the inclusion of several domains to reduce the error margin of fracturing unconventional formations such as the Shilaif. Being an area where field development is rapidly taking place, the inclusion of new technologies have become persistent, and these were evident from the reservoir assessment phase, through to the fracturing phase, and ending with the well testing phase. This level of data gathering and assessment will act as a benchmark for all future unconventional fracturing within the UAE while lessons learnt will further enhance the turnover from drilling to production.
Successful completion and performance of a horizontal well is one of the most dynamic and complex tasks within the oilfield industry, especially when conventional well is an underperformer. Sustaining production from tight reservoirs with conventional stimulation techniques is one of the most challenging tasks. The reservoir of interest is a tight, low permeable carbonate with thin layers. Productivity proven insignificant with considerable in place volume. The objective is to increase and sustain productivity of a pilot well that consists of an open-hole completion. Multi-disciplinary data is reviewed in a systematic way to identify reasons of low productivity and to identify possible solutions. After comprehensive studies and risk assessments, it is concluded to re-complete well with cemented Frac string to perform hydraulic fracturing with Plug and Perf (PnP) technique. This technique is applied within a conventional tight reservoir, allowing for the flexibility of stage count, stage spacing, and multi-cluster design in order to maximize the stimulated reservoir volume (SRV) along 2,000 ft. in upper layer, 1,000 ft. across middle layers and 2,000 ft. in lower layer. In addition, company and service provider collaborated to enhance this design through a zero over-flush technique along with diverting agents. Core, logging data collected from pilot hole is used to build 1D Mechanical Earth Model (MEM), which is further calibrated with MiniFrac performed with Wireline Formation Tester (WFT). A challenge is to avoid Frac height growth towards underlying reservoir, which is separated by dense carbonate layer of 40 ft. Extensive modeling is conducted in order to choose correct Frac design along the lateral in which landing depth is variable in different target layers of interest that added complexities to Frac Fluid selection. Finally, two Frac systems are selected for different segments of the lateral. After running a cemented casing, Six (06) Acid fracturing treatment and five (05) Proppant fracturing treatments are successfully executed in the lower and upper layers respectively. A comprehensive production test is performed to evaluate and compare the testing results of pre and post frac well. To evaluate the contribution of each stage, a Production Logging Tool (PLT) is deployed. The PLT tool shows the contribution and flow distribution across all the clusters and the efficiency of the Frac design and diversion technique/system. This paper summarizes the design processes, selection criteria, challenges, and lessons learned during design and execution phases. It may provide a potential approach for selecting the proper hydraulic fracturing (Acid Vs Prop) and technique (PnP with clusters Vs PnP with one set of perforation). Company has significant portfolio of undeveloped tight carbonate reservoirs with low productivity and considerable volume in place. This technique will pave the way for developing these reservoirs.
The development of unconventional target in the Shilaif formation is in line with the Unconventional objective towards adding to ADNOC reserves. For future optimization of development plans, it is of utmost importance to understand and test and therefore prove the productivity of the future Unconventional Horizontal Oil wells. The Shilaif formation was deposited in a deeper water intrashelf basin with thicknesses varying from 600 to 800 ft from deep basin to slope respectively. The formation is subdivided into 3 main composite sequences each with separate source and clean tight carbonates. The well under consideration (Well A-V for the vertical pilot and Well A-H for the horizontal wellbore) was drilled on purpose in a deep synclinal area to access the best possible oil generation and maturity in these shale Oil plays. Due to the stacked nature of these thick high-quality reservoirs, a pilot well is drilled to perform reservoir characterization and test hydrocarbon type and potential from each bench. Fracturing and testing are performed in each reservoir layer for the primary purpose to evaluate and collect key fracturing and reservoir parameter required to calibrate petrophysical and geomechanical model, landing target optimization and ultimately for the design of the development plan of this stacked play. Frac height, reservoir fluid composition and deliverability, pore pressure are among key data collected. The landing point selected based on the comprehensive unconventional core analysis integrated with petrophysical and geomechanical outcomes using post vertical frac and test results. Well A-H was drilled as a sidetrack from the pilot hole Well A-V. This lateral section was logged with LWD Triple Combo while Resistivity Image was acquired on WL. Based on the logging data the well stayed in the target Layer / formation, cutting analysis data for XRD and TOC was integrated with the petrophysical results in A-H well. Production test results from subject were among the highest rate seen during exploration and appraisal of this unconventional oil plays and compete with the current commercial top tier analog unconventional oil plays. Achieving those results in such early exploration phases is huge milestone for ADNOC unconventional exploration journey in UAE and sign of promising future development.
Following the increase in demand for natural gas production in the United Arab Emirates (UAE), unconventional hydraulic fracturing in the country has grown exponentially and with it the demand for new technology and efficiency to fast-track the process from fracturing to production. Diyab field has historically been a challenging field for fracturing given the high-pressure/high-temperature (HP/HT) conditions, presence of H2S, and the strike-slip to thrust faulting conditions. Meanwhile, operational efficiency is necessary for economic development of this shale gas reservoir. Hence "zipper fracturing" was introduced in UAE with modern technologies to enable both operational efficiency and reservoir stimulation performance. The introduction of zipper fracturing in UAE is considered a game changer as it shifted the focus from single-well fracturing to multiple well pads that allow for fracturing to take place in one well while the adjacent well is undergoing a pumpdown plug-and-perf operation using wireline. The overall setup of the zipper surface manifold allowed for faster transitions between the two wells; hence, it also rendered using large storage tanks a viable option since the turnover between stages would be short. Thus, two large modular tanks were installed and utilised to allow 160,000 bbl of water storage on site. Similarly, the use of high-viscosity friction reducer (HVFR) has directly replaced the common friction reducer additive or guar-based gel for shale gas operation. HVFR provides higher viscosity to carry larger proppant concentrations without the reservoir damage, and the flexibility and simplicity of optimizing fluid viscosity on-the-fly to ensure adequate fracture width and balance near-wellbore fracture complexity. Fully utilizing dissolvable fracture plugs was also applied to mitigate the risk of casing deformation and the subsequent difficulty of milling plugs after the fracturing treatment. Furthermore, fracture and completion design based on geologic modelling helped reduce risk of interaction between the hydraulic fractures and geologic abnormalities. With the application of advanced logistical planning, personnel proficiency, the zipper operation field process, clustered fracture placement, and the pump-down plug-and-perforation operation, the speed of fracturing reached a maximum of 4.5 stages per day, completing 67 stages in total between two wells placing nearly 27 million lbm of proppant across Hanifa formation. The maximum proppant per stage achieved was 606,000 lbm. The novelty of this project lies in the first-time application of zipper fracturing, as well as the first application of dry HVFR fracturing fluid and dissolvable fracturing plugs in UAE. These introductions helped in improving the overall efficiency of hydraulic fracturing in one of UAE's most challenging unconventional basins in the country, which is quickly demanding quicker well turnovers from fracturing to production.
Production of shallow gas has presented a unique opportunity to implement a fit for purpose fracturing workflow due to the level of complexity these reservoirs present. Initially acquired logging data including open hole logs, mud logs, wireline pressure measurements and reservoir sampling as well as micro-frac readings confirmed the presence of relatively shallow gas in low permeability rock. Hence introducing fracturing as a favourable method of extraction made it imperative to address the level of complexity within the reservoir, which varied from the presence of anhydrites, extreme heterogeneity, water sensitivity, as well as the fault environment at such shallow depths. Exploring pilot holes and running advanced image logs as well as acoustic measurements along with micro-frac operation, provided critical data for completion design improvement to not only enhance the chances of successful placement, but also increase the overall gas output. The relatively low bottom hole static temperature and pressure, soft rock, heterogeneity and overall immaturity of the reservoir required extensive core flow tests. X-Ray Diffraction (XRD) as well as lithology scanner logs were also used to fully understand the complex mineralogy. A suitable salt tolerant fluid was proposed for fracturing before optimisation as well as the inclusion of fit for purpose acid systems. The workflow also utilised the extensive geomechanical datasets for analyses, as well as incorporating the geological and petrophysical interpretations. This was followed by sensitivity analyses of the fracturing design based on size of stages, stage spacing, cluster spacing, as well as the cement quality. After performing micro-fracturing tests, a one dimensional mechanical earth model (1D MEM) was optimised to enable better understanding the fracture geometry. The workflow also included the use of chemical tracers to qualify the success of each fracturing stage within the target horizontal section. The workflow started with a collaboration between geology, geomechanics, petrophysics, reservoir, as well as stimulation domains, which resulted in the completion of the first horizontal multistage fracturing completion within the targeted shallow gas reservoir. This milestone provided insight into the required planning for future gas wells within the region and has left significant potential for optimisation given the complexity of the reservoir. The consolidation of a workflow to deliver the first shallow gas project in order to extract the initially confirmed gas presence has presented a novel approach to such a niche project. This was initiated by utilising a time-lapse image analysis, petrophysical and reservoir evaluation, and then coupled with the introducing propped fracturing and matrix acidizing to further calibrate log-deduced parameters. A high level of detail in core analysis, as well as micro-fracturing interpretations, have reduced the uncertainty regarding fracture generation, initiation, and fracture extension into the far field in such a shallow and unconsolidated, low temperature and pressure reservoir.
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