The paper aims to present the successful execution of the first offshore multilateral well completed for multistage high-pressure proppant stimulation - in the Black Sea, offshore Romania. The paper describes the drivers that lead the operator to trial a multilateral well as well as cover the considerations made in selecting, defining and executing the final completion solution with a review of the lessons learned. With only one platform slot left and a significant undrained area of reservoir the operator had to maximise the hydrocarbon recovery through a single well which, due to pressure to increase the operator's daily production, had to be finalised in just one year. Building on field experience gained since 2008 in drilling and completing for multistage proppant stimulation a detailed screening and evaluation of multilateral completion technologies was performed. The focus was on developing a concept that would minimise risks during execution while meeting cost and lead time objectives, which necessitated customising the chosen TAML Level 3 completion design and installation methodology. To maximise rig-time efficiency the well was executed in two phases: 1) drilling and lower completion installation of both branches with a drilling rig and 2) stimulation and upper completion installation with the platform's workover rig. With six stages in each lateral the high-pressure stimulation was executed by a converted supply vessel in four sailings, necessary to reload materials. To meet the delivery schedule, ensure simplicity and utilise operator experience the completion was realised with no dedicated multilateral hardware, rather, through the effective use of standard multistage stimulation open hole completion equipment and appropriately engineered bent joints to exit the main bore. With initial production rates higher than anticipated, the multilateral well completed in this manner has proven to be considerably more economic than drilling two horizontal wells with equivalent reservoir coverage. The success of this well serves as a proof of concept and provides increased confidence in delivering reliable, cost effective multilateral wells even under tight time constraints and in areas and/or operators with no history of multilateral well completions
This paper presents an analysis of the stimulation treatment design and operational efficiencies in the Black Sea. In greater detail, the paper focuses on how the stimulation design and each operational step has been optimized to save time, money and ensure an HSE driven completion methodology. An analysis was performed on the stimulation design and implementation approach looking at its evolution through a knowledge building and lesson learning process. The principal goal was to determine the most economical way to stimulate an offshore well without making any concessions to the reservoirs’ production or ultimate recovery. From the basics of well and frac design to completion optimization, effort was applied in analyzing ball launching procedures, frac spacing, logistical arrangements on the stimulation vessel and all other areas where there was potential to make improvements. Ultimately, an analysis of fluid displacements during flush was performed and deductions inferred. Past stimulation treatments were analyzed in an effort of better understanding the advantages and disadvantages in terms of production output of the wells. Similarly, an analysis of the completion approach and operational efficiencies showed the ability of pumping three stimulation stages a day. Considering that horizontal wells in the area are usually completed in six stages, a stimulation campaign would effectively be completed in 2 pumping days, 4 days total if no weather or operational delays are faced. Further improvements of this approach have been implemented in 2021 when six stimulation stages have been pumped in a single vessel ride. Applying the ball drop procedure offshore showed optimal results, as it is efficient in reducing downtime in between fracturing stages and in achieving proper isolation between stimulation zones. Likewise, with over flush being a concern throughout most of the stimulation population, certain cases in the Black Sea showed that over flushing did not adversely affect production of the wells with the production exhibiting ~15% above expected production rates post stimulation. In conclusion, the authors believe that the operational efficiencies achieved in the Black Sea are transposable in other offshore environments and successful cost cutting can be achieved by sound engineering and logistical decisions. The approach and results are beneficial in understanding where the economics are positively impacted in multistage stimulation treatments in the offshore environments, hence ultimately improving the rate of return.
Increased production alongside low costs has always been a long-standing goal for operators in a time where the industry is thriving to increase their operational and economical efficiencies. For maturing fields, operators are constantly seeking innovative techniques to access large quantities of reserves found in low permeability formations. The nature of the reservoir has resulted in an economical need to implement a hydraulic fracturing campaign. This would assist with increased production through wider contact area of the producing interval. After a campaign resulting in favorable results through hydraulic fracturing, additional efficiencies addressing the operational and cost concerns of cemented plug & perf were required. In order to maintain production increases while maintaining operational efficiency, the need for multi-stage hydraulic fracturing became evident. Six candidate wells were selected for proppant fracturing utilizing a multi-stage completion technique that has been widely adopted in North America for the past 17 years and internationally for over a decade. The technique utilizes a series of hydraulic mechanical packers and fracturing ports that are shifted open sequentially across the applicable zones targeted for treatment. The ports have seats that are sized to respective balls, which are used to isolate the stimulated intervals. The system allows for increased efficiency through eliminating the risks associated with wireline operations for perforating, or coiled tubing operations to mill out bridge plugs. It also allows for immediate and simultaneous production from all stages as well as contingencies for shutting off water zones. From June 2016 to March 2017, six systems were installed consisting of 6 to 8 hydraulic fracturing stages, which were placed in cased-hole pre-perforated wells. This paper investigates reservoir quality assessment as well as the stimulation efficiency and productivity enhancement of the Sidri Field. It investigates two different completion methodologies to investigate operational efficiency and productivity enhancement of the Sidri Field in the Sinai Peninsula. The comprehensive evaluation will involve discussions of candidate selection, pre-job design alongside comparisons of timeline, cost, zonal isolation, and productivity to help serve as a guideline for operators in the region looking to enhance their completion approach.
Recently two multilateral horizontal wells have been completed offshore using dedicated multistage hydraulic fracturing completions. The first well, located in the Central North Sea (referred to as ML-CNS), was stimulated using acid fracturing; while the second well, located in the Black Sea (referred to as ML-BKS), was stimulated using proppant fracturing. This paper presents the different drivers, challenges and lessons learned for each well while emphasizing the well construction and stimulation methodologies developed for the different reservoirs and field characteristics. The field development drivers for drilling and completing these offshore hydraulic fractured multilateral wells, a first of their kind globally, was different for each case. The objective of the first project, initially considered uneconomic, was to engineer a technical solution for completion and production of two separate reservoirs with only one subsea well. The second project was seeking to optimize infill drilling from the last available slot on the offshore platform to maximize reservoir contact and production in the same reservoir. ML-CNS was a TAML Level 2 completion with a 14-stage, 5 ½" multistage completion run in each lateral and set-up for sequential acid fracturing. Operationally, the first lateral was drilled and stimulated, followed by the drilling and stimulation of the second lateral, using the drilling whipstock to navigate through the multilateral junction. ML-BKS was a TAML Level 3 completion that had a 6-stage, 4 ½" multistage completion installed in each lateral, which were proppant fractured following a sequence designed to minimize the jack-up rig time required. Both legs were drilled and completed prior to starting the stimulation, access to either lateral was achieved with the existing workover unit on the platform by manipulating a custom designed BHA. The lessons learned from the first project executed in the North Sea were able to be transferred and applied to the second project in the Black Sea to allow for a more efficient and confident completion solution. Led by varying economical and regional constraints, the key factor for both wells centered on delivering operationally simple and reliable multilateral completion designs to economically meet the field development strategy in place. To the knowledge of the authors and following subsequent literature research, both wells are a worldwide first for an offshore multilateral well completed with multistage acid fracturing and multistage proppant fracturing, and together they represent a new trend in cost-effective offshore field development through well stimulation. The successful case studies for both wells with the combined analysis of the benefits, challenges, and lessons learned will provide a guide and instill confidence with operators who find this approach beneficial with a view to applying it in other assets.
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