An Expanded Study of Proppant Distribution Trends from a Database of Eroded Perforation Images

This paper further develops an analysis of proppant distribution patterns in hydraulically fractured wells initially presented in SPE-199693-MS. A significantly enlarged database of in-situ perforation erosion measurements provides a more rigorous statistical basis allowing some previously reported trends to be updated, but the main objective of the paper is to present additional insights identified since the original paper was published. Measurements of the eroded area of individual perforations derived from downhole camera images again provide the input for this study. Entry hole enlargement during limited entry hydraulic fracturing provides strong and direct evidence that proppant was successfully placed into individual perforations. This provides a straightforward evaluation of cluster efficiency. Perhaps more importantly the volume of proppant placed into a perforation can also be inferred from the degree of erosion. Summing individual perforation erosion at cluster level allows patterns and biases to be identified and an understanding of proppant distribution across stages has been developed. Outcomes from an analysis of a database that now exceeds 50,000 eroded perforations are presented. Uniform reservoir stimulation is a key objective of fracture treatments but remains challenging to measure and report. The study therefore focused on understanding how uniformly proppant is distributed across more than 1,800 measured stages. Results demonstrate how proppant distribution within stages is influenced when treatment parameters change. Our approach was to vary one parameter, for example the stage length, while all other parameters were maintained at a consistent value. We investigated multiple parameters that can be readily controlled during treatment design and show how these can be manipulated to improve proppant distribution. These included stage length, cluster spacing, perforation count per cluster and perforation phase. Hydraulic fracturing is a complex, high energy process with numerous input parameters. At individual cluster and stage level outcomes can be unpredictable and diagnostic results are often quite variable. The approach taken here was to complete a statistical analysis of a sufficiently large dataset of in-situ measurements. This allowed common trends and patterns to be confidently identified and conclusions reached on how proppant distribution is affected by varying specific design parameters. This should be of interest and value to those designing hydraulic fracture treatments.

A State-of-the-Art Approach to Unlock the Potential of Complex Sour Reservoirs in Southern Oman During Global Market Downturn

Recent years and especially the coronavirus pandemic have been very challenging for the oil industry, resulting in a significant reduction in investment, forcing companies to review budgets and search for more efficient and economical technologies to achieve the target level of hydrocarbon production and revenue generation. In PDO, one of the most challenging fields is "AS", where extreme downhole conditions require a very well-engineered approach to become economical. This field has already seen some of the most advanced technology trials in PDO that are also covered in multiple SPE papers. Based on the new approaches and techniques that were successfully implemented on recently drilled wells, it was decided to review the older, previously fractured wells in the area and assess them for a refracturing opportunity. The main challenge in this project was that these older wells were previously hydraulically fractured in multiple target intervals, therefore both zonal isolation and successful placement of the new fracs were becoming the major concerns. As the planned coverage by the new fractures was to ensure no bypassed pay, the only applicable technology on the market was a pinpoint fracturing process, whereby the targeted placement is achieved through limited entry perforations and focused energy of the injected fluid. The subject pinpoint technology anticipates that the limited entry sandblasting perforation is created and then proppant laden fluid is pumped through a sandblasting nozzle which is part of either a coiled tubing (CT) or a jointed pipe (JP) Bottom Hole Assembly (BHA), and the backside (or the annulus of the injection path) is used to maintain the positive backpressure from the top. This technology allows for choosing a desirable order of target interval selection inside the well, unlike conventional plug and perf or a simplified multistage completion, where the treatments must be placed only in order from bottom to top. Another advantage of this approach is a faster frac cycle through the elimination of wellbore cleanout requirement. Being a unique and first-ever application in the Middle East, using CT for placing frac treatments through a jetting nozzle demonstrates the full scale potential of this approach not only in conventional wells but also in complex, sour and High Pressure (HP) environments that are often found in the Sultanate of Oman and in the Middle East. This paper will cover the advantages and disadvantages, complexity and requirements, opportunities and lessons learnt in relation to this approach.

Casing Deformation Mitigation Achieved Through Ball Activated Sliding Fracturing Sleeves – An Alternative to Plug and Perf Fracturing Operations

Casing Deformation has plagued numerous unconventional basins globally, in particular with plug-and-perforation (also known as plug-and-perf) operations. This infamous issue can greatly influence 20-30% of field productivity of horizontal wells in shale and tight oil fields (Jacobs, 2020). When a wellbore lies in a target zone and intersects many natural fractures, these fractures are perturbed by hydraulic stimulation. Therefore, rock or bedding slippage may occur, resulting in casing deformation. This phenomenon is escalated by active tectonics, high anisotropic in-situ stresses, and poor cement design. This paper evaluates the mechanisms of casing deformation. It reviews how these conditions can be evaluated in the target zone. The mitigation procedures to reduce casing deformation through either well planning or completions design are discussed. Finally, an alternative completion method to plug-and-perf allowing limited entry completion technique in restricted casing with a field case study will be discussed.

First Multilateral Well in the Most Congested Field in Abu Dhabi, Case of Study

This paper will highlight the first level 2 Multi-lateral well in BAB Field with permanent limited entry liner completion in the lower borehole to enhance accessibility and production. The well presents a technical milestone to the company in the development of multiple reservoir by combining two (2) wells from different reservoir and produce from both by using same surface well construction. At initial stage, the economics related to the implementation of the multilateral approach were analysed. Calculation was done by comparing the cost related to the technology application against the cost to prepare one (1) location plus completing a well up to the 7″ liner and mobilizing the rig twice. Then, it was necessary to select the candidate wells to be drilled from the same slot where synergy between Study team and drilling team was in place in order to ensure proper target alignment to make feasible the drilling and completion operations at the same time that the production targets were fulfilled. This project confirmed the feasibility of multilateral well application in a very congested field in terms of wells construction and surface facilities. In order to achieve such goal full synergy must be in place to select proper wells candidates and align targets. Cost reduction is massive considering the elimination of three (3) well phases plus avoidance of one (1) location construction and also the elimination of 1 rig move represents a big impact in terms of economics. Furthermore, the impact in terms of the risk reduction must be considered By combining two (2) wells in one (1) and eliminating three (3) phases in the standard well construction the harmful impact of location preparation, drilling fluids and cuttings on the environment is reduced by 45%, especially with oil base mud system. Geological problems can be observed during drilling each phase of a new well. However, drilling multilateral wells will reduce this occurrence. Well was completed with 7″× 4-1/2″ top packer, 4-1/2″ Slotted tubing and seven (7) swellable packers in lower borehole as well as Dual upper completion with 7″ single retrievable and 9-5/8″ dual retrievable packer and 2-7/8″ and 3-1/2″ tubing combination in both short and long string. This paper presents ADNOC Onshore first and successful experience in the deployment of new acquired technology for the Drilling multi-lateral / dual completion systems in BAB Field. The screening criteria for selecting the system as well as the benefits realized and lessons learned from this experience are also discussed together with the design simulations required to ensure the success of the well construction.

ADNOC's Smart Liner Initiative – A Step-Change in Matrix-Acid Stimulation Efficiency

ADNOC is progressing with large-scale rig-less high-rate matrix stimulation by deployment of advanced lower completions. A key contribution to future production growth is expected to come from these "Smart Liners" that rely on the principles of the limited-entry technique. The concept is based on a number of small, pre-drilled and unevenly spaced holes which enable an even distribution of acid along the entire reservoir drain to be stimulated. The smart liner incorporates swellable packers to avoid annular flow of acid to preferential zones and to isolate segments with heterogeneities. In this work, we focus on aspects related to planning, design and execution of high-rate matrix-acid stimulation of wells. We demonstrate that short wells need a different design approach compared to extended-reach wells and we provide guidelines on how to achieve the highest achievable pump rate and desired acid volume subject to reservoir, well and equipment constraints. The carbonate reservoirs typically exhibit considerable variation in permeability along the well, hence techniques for production profiling, such as inline tracers, are valuable for assessing the actual stimulation effectiveness. Wormhole penetration for a particular acid system will vary depending on the rock petrophysical properties and the reservoir properties; therefore, a systematic data analytics project is on-going.

Holistic Customized Approach to Address Practical Challenges for the Large Scale Implementation of Limited Entry Liners Completions at ADNOC Onshore Fields

Limited entry liners (LEL) implementation strategy is one of the key solutions to to improve the well productivity by maximizing the reservoir contact and matrix stimulation carbonate reservoirs. This strategy requires conducting high rate and high volume acid stimulation with high pressure pump after the installation of limted entry liner, that poses practical concerns to be addressed for adopting conventional well completions and existing resources. In addition, implementation of the LEL completion and stimulation for a large scale application within the minimum time frame and limited resources is a challenge. This paper provides the detail of challenges faced and solutions adopted to implement the LEL completions amd stimulation at onshore fields. Challenges including suitable candidate selection, completion design, limited materials for well construction to handle high-volume acid stimulation, limited well head injection pressure, contractual limitations for securing the tools and pumping equipment. Further, this paper discusses about the temporary solutions adopted for executing the LEL implementation in the best economical way within near future and provide the long term solutions for LEL implementation in the next 5 years business. The first three LEL completion wells that were successfully installed and stimulated at ADNOC Onshore are currently producing at more than 2 times higher PI (productivity index) compared to the pre-stimulation rate. The same apply to the injector wells, in which significant improvement on the injection rate of up to 18bbl/min (26000 bwpd) was observed. Currently ADNOC Onshore is planning to execute the LEL completion and stimulation in additional 15 wells during 2021 along with plan for up to 300 LEL completions during the next 5 years. The LEL technology is a key technology to support ADNOC lower completion strategy which aim to minimize the bare foot completions in order to increase the horizontal wellbore accessibility and effective stimulation. Overall, the first LEL installation and stimulation completed within 8 months from the candidate finalization using the existing resources available in ADNOC Onshore. This paper describes an economical solution for implementation of LEL completion strategy at large scale for major fields within minimum time frame by utilizing the existing resources while adhering to HSE rules.

A World-First: 3-Legged Lateral with Smart Completion, Smart Liners and Inflow-Tracers Across Low-Permeability Multi-Stacked Reservoirs

In a giant, mature UAE offshore field, consisting of complex multi-stacked heterogeneous reservoirs, the western part has been less developed, due to contrasted reservoir properties and low-permeability layers. The development in that part of the field was re-visited, to account for reservoir challenges and surface limitations. The objective was to achieve production mandates, understand reservoir behavior, while minimizing well count and expenditures associated with interventions and surveillance activities. To evaluate this challenging area of the field, a unique multi-lateral well was designed, targeting three distinct reservoirs, and allowing to concurrently produce and understand them in a viable manner. The reservoirs have poor characteristics, with permeability lower than 10 mD, except for the deeper one, which has some high permeability streaks. Accounting for the tight formations, each horizontal leg had to be stimulated efficiently, despite being inaccessible with coiled-tubing. In addition, well production had to be reliably back-allocated to each drain, and meet pre-defined reservoir guidelines. Despite contrasting properties, all three drains had to be produced at reasonable rates, avoiding that one drain would dominate the other two. And finally, enhanced reservoir understanding was required within each drain, with qualitative indication of their flow profile and associated reservoir conformance. The 3-legged multi-lateral oil producer was drilled and completed successfully. In each of the three horizontal laterals, totaling more than 15,000 feet length, drop-off limited-entry ‘Smart Liners’ were installed, to allow bull-heading stimulation. This offered an effective high-volume matrix acidizing method, adapted to the contrasted properties and tight zones encountered along the laterals. The well was equipped with permanent downhole gauges and inflow control valves (ICV's) to dynamically monitor downhole contributions, modulate production from each drain, avoiding well delivery to be dominated by the highest potential reservoir and control unwanted water/gas production to the surface. To complete the picture, chemical in-flow tracers were installed, in the tubing and within each drain, to monitor the laterals’ flow profiles and performance, and measure the individual contribution from each reservoir. This aimed to determine the efficiency of the ‘Smart Liners’ design and proved a cost-effective option to quantify the contribution from the laterals, compared to running regular PLTs. The resulting pilot is the first well in the world to combine a smart completion with three limited entry ‘smart liners’ utilizing drop-off technique and chemical inflow tracers. The pilot well, which behavior is being evaluated over 2021, provides a groundbreaking approach to evaluate and unlock hydrocarbon resources in a poorly developed area of the field, allowing a significant optimization of well count and of associated capital and operating expenditures.

First Permanent Inflow Monitoring Experience in a Smart-Liner, Intelligent-Completion, Multi-Lateral Adnoc Offshore Well

The scope of this paper is to share a field experience with permanent inflow tracer deployment and monitoring of an intelligent multi-lateral well, completed with Smart-Liner (Limited Entry Liner). It will describe what ADNOC Offshore has learnt through inflow tracing clean up surveillance from several restarts and steady state production through inflow modelling interpretation techniques. This passive method of permanent monitoring technology utilizes chemistry and materials expertise to design tracers that release signature responses when they come into contact with either in-situ oil or formation water. The chemical tracer technology enables wireless monitoring capabilities for up to five years. Unique chemical tracers are embedded in porous polymer matrix inside tracer carriers along select locations in the lower completion to correlate where the oil and water is flowing in a production well. Interpreting tracer signals can provide zonal rate information by inducing transients to create tracer signals that are transported by flow to surface and captured in sample bottles for analysis. The measured signals are matched with models through history matching to yield zonal rate estimates. ADNOC Offshore has installed inflow tracers in an intelligent multi-lateral well to monitor laterals’ contributions, to verify new completion technology, and to estimate the flow profile from individual sections of Smart-Liner, run for the first time in the field. The interpretation results have been able to characterize inflow performance without any intervention in the well. Several restart and steady state surveys are planned to understand some key characteristics of the well completion and reveal how the well has changed since it was put on production. This technology will help allocate commingled production to the three laterals. The use of inflow tracers will provide multiple inflow surveys that will reduce operational risk, well site personnel, costs and will improve reservoir management practices. Permanent inflow tracing is expected to change the way production monitoring can be performed, especially in advanced wells where PLTs or Fiber Optic technology cannot access multi-laterals.

Numerical Simulation of Multi-Cluster Fracture Propagation In Horizontal Wells With Limited-Entry Designs

The effective propagation of multi-cluster fractures in horizontal wells is the key to the development of unconventional reservoirs. Due to the influence of pressure drops at perforating holes and the stress shadow effect, it is difficult to predict the fracturing fluid distribution and fracture dimensions in a fracturing stage. In this paper, a two-dimensional fluid-solid coupling model for simultaneous propagation of multiple fractures is established, and fluid distributions and dimensions of multiple fractures are studied with respect to different perforation designs. The model combines the User Amplitude Curve Subroutine (UAMP) in ABAQUS and the cohesive zone model (CZM) to calculate the perforating friction, fluid distribution and fracture propagation behaviors. After the accuracy of this model is verified by the analytical solution, a group of simulation is conducted to compare fracture propagations when the conventional limited-entry method (CLE) and extreme limited-entry method (less than 5 perforations per cluster, XLE) are used. Simulation results show that the edge and sub-central fractures in CLE cases almost get all the fluid and effectively propagate; central fractures receive little fluid and hardly propagate. In XLE cases, the fluid distribution of each fracture is relatively uniform, but the fracture lengths within one fracturing stage is still uneven; however, only reducing numbers or radii of perforation holes cannot achieve the uniform fracture propagation, where diverters might be further needed. Findings of this study provide a reference for the perforation optimization of multi-cluster horizontal wells in the field.

Practical Quantification of Sand Distribution from Perforation Erosion Measurements, An Example from Marcellus Shale

Unconventional wells require hydraulic fracturing to be economic. Several levers for improving well productivity are available including stage spacing, cluster spacing, and sand loading however much of the recent focus has been on perforation design as well as a more uniform distribution of sand and water. This paper proposes to evaluate how optimizing the perforation strategy might enhance stimulation distribution along the lateral, in the Marcellus shale. Three different perforation designs were tested for better understanding of perforation efficiency, when considering design options such as perforation diameter, tapered perforating, and Extreme Limited Entry (XLE). A combination of step down tests, downhole perforation imaging and modeling are used to compare the different designs and support the conclusions. Downhole ultrasonic perforation imaging, even if it only captures an end-of-job snapshot, provides valuable insight to the dynamics of limited entry perforating and sand distribution. The pre-fracture diameter is identified as a key uncertainty, while post-fracture measurements show variations from the specifications of the shape charge and, in some instances smaller perforation diameters when compared to the expected value. The current dataset allows for a better understanding on the concept of erosion and how to correlate erosion with actionable design parameters such as perforation diameter or rate per perf. Downhole ultrasonic measurement of the perforation exit diameter, along with the corresponding erosion assumptions, are combined with modeling to recreate the rate and pressure evolution along the fracture stage., In addition, one can infer the actual volume of sand placed in each cluster in order to provide a quantitative assessment for future performance evaluation.