
 One of the most giant offshore multi-reservoir oil fields in the world has been developed using vertical, deviated and short horizontal wells drilled off-shore from wellhead platform towers. Towards the concept of cost optimization, further redevelopment of the oil field was planned using extended-reach long horizontal wells with throws greater than 18,000 ft and measured depths greater than 25,000 ft with some wells exceeding 35,000 ft, from artificial built islands by reducing the number of wells required to drain the reservoir with improving recovery. In order to enable transition to such concept, new well design strategic concepts were required to come up with the robust well completion design (both upper and lower completions) that is expected to be fit-for-purpose for 30+ years – well life time. Lots of uncertainties and challenges are faced in order to get to the goal of understanding different reservoirs behaviors such as, for better reservoirs development relying on dynamic reservoir models combined with actual geological, petrophysical, seismic and production data. Each piece of information yielded a certain potential that led to a certain completion design based on available data and expectations.
 This paper will discuss the upper and lower completion designs, execution and performance from production engineering perspective to maximize productivity for the whole life cycle of this long horizontal wells. The extended lateral length in these wells warrants innovative designs in upper and lower completions as traditional completion designs no longer valid in addressing the challenges in these wells. The key well design and planning process involves designing the upper completion – tubing, gas lift system, downhole gauge and lower completion liner – Pre-perforated liner (PPL), Limited-entry Liner (LEL) or Inflow Control Devices (ICD) with annular isolation with packers, efficient initial start-up and clean up strategy, regular monitoring well performance and surveillance (e.g. downhole pressure monitoring, PLTs, fluid sample analysis etc.). The paper will also address the challenges in long horizontal wells such as accessibility, production/injection conformance and effective stimulation of the laterals.

A Robust Production Engineering Strategy for Extended Reach Well for Sustained Performance


 
 
 A new vision with new techniques of wells’ upper and lower completions have been applied successfully throughout a giant offshore multi-reservoir oilfield. Wells with long to very-long laterals have been completed successfully following a systematic strategy based applications and showed tremendous success. This paper will present the various techniques used completing wells in different reservoirs considering well-integrity and HSE regulations in order to achieve the maximum wells’ deliverability’s at their lowest costs throughout the well life. Many challenges were faced and overcame in order to reach the optimum completion that suits each well. A complete journey from reservoir simulation to well and network models, well performance to reservoir management studies, from geological models and interpretation to geo-science and seismic inputs, in addition to actual production data, all helped to achieve the over-all target. From the phase of design to the phase of implementation and beyond to the production phase, each piece of information yielded a certain potential that led to a certain completion design based on available data and expectations.
 
 
 
 This paper will discuss the new innovative upper and lower completion designs’ strategies along with the execution and performance from production engineering perspective in order to reach the maximum productivity for the life cycle from these long horizontal wells at the lowest possible cost. The extended lateral length in these wells warrants innovative designs in upper and lower completions, as the traditional completion designs no longer suite to address the challenges in these wells. The key well design and planning process involves designing the upper completion including suitable tubing size with the most effective and durable gas-lift system, and lower completion liner designs for different wells’ cases. Efficient initial strategies to start-up wells including some protocols with well-performance monitoring and reservoir surveillance. The paper will also address and discuss the challenges in long horizontal wells such as accessibility, production/injection conformance, and effective stimulations of these laterals.
 
 
 
 This paper will discuss and show many examples of the completed wells with different types of completions and a comparison of their performances after initial startup and during the back-flow period in addition to the extended performance during normal flowing conditions. Some LEL wells were logged and stimulated showing excellent results; these results will be shared in the paper. It is concluded that the LEL completion proved itself to be the future for lower completion to be widely used in the field.
 
 
 
 The novelty of such new applications were that they were designed in-house and applied on considerable number of long lateral wells showing excellent results that is changing the completion future strategy in the field and may be in the region or even worldwide.


Strategic Engineering Application for Long Lateral Wells

Long horizontal or highly deviated wells require lower completion liners to improve well and reservoir management of the carbonate reservoirs in ADNOC's portfolio. Optimum well productivity depends on effective stimulation post drilling. Traditionally, a complicating factor in a matrix-acid stimulation treatment has been poor control of the acid placement along the reservoir section to total depth (TD) without stage equipment or chemical diverters. The limited-entry liner (LEL) lower completion addresses the shortcomings of other stimulation techniques. It consists of a number of unevenly spaced holes with the purpose to distribute acid evenly along the reservoir section to be stimulated. ADNOC is planning to execute a series of pilots to test and possibly expand the operational envelope of the LEL technique.Design of a the hole-size distribution requires a mathematical model, which accounts for the various pressure drops encountered in the system as well as the impact of the chemical reaction between acid and rock. In this work, we present a comprehensive algorithm for designing a hole-size distribution which yields a user-specified acid coverage and also provides the best possible wormhole penetration, subject to a number of constraints related to surface pressure, pump rate, and acid volume available. We make use of findings published over the past 15 years in the SPE literature to arrive at an enhanced design philosophy, which is appropriate for the carbonate reservoirs in ADNOC's portfolio.The design model takes into account a number of important parameters, including fluid and reservoir properties, as well as completion information such as tubing ID, liner ID, and the LEL hole sizes. A check is made using nodal analysis software to ensure that the LEL completion does not act as a flow restriction during back-production.

A Comprehensive Model for Acid Stimulation of Lower Completions


 A giant carbonate field offshore is being redeveloped using extended-reach horizontal laterals, up to more than 20,000 ft. with open-hole un-cemented liners, drilled from artificial islands. Previously, SPE171800 introduced an innovative Limited-Entry Liner (LEL) design that enables high rate aggressive stimulation of these wells by bullheading. These wells provide significant profitability in unit development cost, though it is critical to effectively stimulate the entirety of the long laterals to maximize reservoir recovery. Recently, Sau et al. 2019 presented our first application of real-time fiber optic surveillance during the successful stimulation of a water injection well with a 12,000 ft LEL lateral section. Fiber optic distributed temperature and distributed acoustic sensing (DTS/DAS) data were collected. Qualitative analysis of the real-time data were compared with a subsequent production logging tool (PLT) to confirm the effectiveness of the LEL completion and also the validity of the real-time fiber optic data.
 This current paper describes the detailed analysis of the DTS/DAS dataset collected and the information that can be extracted from it regarding the effectiveness of the well stimulation. Also presented here is how DTS/DAS can be used to monitor the completion performance during injection; quantitative DTS/DAS analysis provides detailed insight into the acid volume injection into each compartment as well as post-stimulation water injection profile over time and at different injection rates. Recommendations are made regarding how to use the data from future DTS/DAS enabled stimulation jobs to extract the most value from real-time measurements and how permanently installed fiber optic DTS/DAS systems can be used to monitor the health and performance of such extended-reach injection wells.

First Real-Time Fiber Optic Surveillance and Analysis of a Bullhead Stimulation of an Extended-Reach Horizontal Lateral in a Giant Offshore Carbonate Oil Field

\n Horizontal steam injectors can improve the efficiency of thermal operations relative to vertical injectors. However, effective in-well and reservoir surveillance are needed to understand steam conformance. Uniform steam-chest development improves the steam/oil ratio in continuous steam injection and accelerates recovery in cyclic steam injection. The conformance of the injected steam can be achieved by flow control devices (FCDs) deployed on either tubing or liner. A new liner-deployed FCD was used in a horizontal steam injector in the Kern River field. The liner-deployed FCD is intended to replace the tubing-deployed FCDs while reducing capital costs, surveillance costs, and well intervention costs for conformance control.\n Fiber optics was used for surveillance, which is the most promising method in horizontal steam injectors considering reliability, accuracy, and cost. Fiber optic data enables monitoring the performance of liner-deployed FCDs as well as estimating the flow profile along the lateral length. Multimode distributed temperature sensing (DTS) optical fibers and single-mode distributed acoustic sensing (DAS) optical fibers were installed in the well for these objectives. Algorithms for interpreting DTS were improved to include a new technique, shape language modeling (SLM), and a probabilistic approach. The configuration of the FCDs was changed during the first well intervention, and it was monitored by DTS and DAS. Data from both DTS and DAS confirms the open/closed position of the sliding sleeve of FCDs initially and after the intervention. The probabilistic estimates of steam outflow in several FCD configurations match well with the theoretical outflow that is expected from the critical flow of steam through chokes installed in the FCDs.

Flow Profiling Using Fiber Optics in a Horizontal Steam Injector with Liner-Deployed Flow Control Devices


 Earlier, SPE Technical Paper 193036 introduced the development, testing, qualification and deployment of plugged liner technology in Extended Reach Drilling (ERD) field re-development from artificial islands of a giant offshore field in the United Arab Emirates (UAE). This paper will highlight the excellent well performance of the two pilot wells and other island wells with this technology deployment and the significant impact of this technology on initial production rates as well as reservoir recovery.
 Plugged LEL technology utilizes Dissolvable Plugged Nozzle Assemblies (DPNA) for deployment with Limited-Entry-Liner lower completions combined with Remote Close Shoes (RCS). The technology results in about 5 days of rig-time saving in well displacement process in extremely long laterals, switching from the non-aqueous reservoir drilling fluid to an aqueous completion brine, by eliminating the use of a dedicated liner displacement string.
 Two pilot wells with extra-long horizontal laterals in the very low permeability region were completed with plugged LEL utilizing (1) 169 DPNA 4-mm in 28 zones isolated by swell-packers and (2) 183 DPNA 4-mm in 24 zones isolated by swell-packers. The distribution and location of the DPNA holes along the liner are designed in-house with ExxonMobil proprietary software.
 After successful deployment of the plugged liner in two pilot wells which resulted in significant CAPEX reduction upfront through reduced duration for well construction, the well performance was monitored closely in order to assess the success of the technology application in terms of production and reservoir objective. The production rates from both pilot wells exceeded the expected production rates. Apart from total production rate, the critical component of this technology was to ensure all the dissolvable nozzles that plug the liner have dissolved across the lateral enabling lateral conformance which is key to initial production rate and reservoir recovery. Thus, production logging tool (PLT) was performed and the results indicated that the entire extended production lateral is contributing to flow. Apart from well construction cost savings, this technology also enables enhanced wellbore cleaning and improved filter-cake breaker placement. These enhancements resulted in improved well performance than expected and lateral conformance which maximizes reservoir recovery from horizontal wells. After the success of the first two pilot wells, field-wide deployment of the plugged liner was initiated and several wells have been completed with this technology.
 This paper will demonstrate the success of the first global deployment of a novel lower completion technology – plugged nozzles LEL - to maximize production and recovery in ERD wells with very long laterals. Value and impact of this technology will be presented in terms of well performance, reservoir recovery in addition to previously highlighted well construction cost savings.

Advanced ERD Lower Completion Technology Performance Update in a Giant Offshore Field UAE


 A giant carbonate field offshore Abu Dhabi is being redeveloped using extended-reach-horizontal-laterals up to 20,000 ft with open hole un-cemented liner, drilled from artificial islands. Long horizontal wells provide significant profitability in unit development cost; however it is critical to ensure effective stimulation of the complete lateral to maximize reservoir recovery. Earlier, SPE171800 introduced an innovative liner design for long open hole horizontal completions, namely Limited-Entry Liner (LEL) that enables high rate aggressive stimulation by bullheading technique. This paper will present the field stimulation results of more than five LEL laterals ranging several-kilometers in open hole completions, demonstrating the impact of LEL stimulations in accelerating production and maximizing reservoir recovery.
 Several LEL horizontal wells were completed in low-permeability rock to enable high rate bullhead matrix stimulation. ExxonMobil proprietary software is used to design fit-for-purpose LEL that enables acid injection conformance along the lateral and at the same time creates deep-wormholes by high-velocity acid-jets through 3-mm/4-mm holes in liner base-pipe distributed non-uniformly along the lateral, compartmentalized with oil/water-swellable-packers. The execution of the stimulation campaign was made possible through the use of modularized-equipment packages installed on an ADNOC-vessel, utilizing a unique mechanism that locks the package components to frames installed to the vessel-deck. The stimulation package consists of 6×2000HHP pumps delivering up to 60bpm at 10,000psi. The liquid-additive system, 140bbl vertical mixing tank and more than 190,000gallon raw-acid storage tanks are fully automated to enable acid mixing and pumping on the fly at the desired rates, concentrations and recipes.
 In order to demonstrate the effectiveness of acid placement and effective stimulation across the entire lateral, real-time Fiber-Optic surveillance techniques (DTS-DAS) were utilized. The recorded thermal and acoustic profiles provided a qualitative and quantitative measurement of the effectiveness of the mechanical diversion delivered by the LEL design. These data will help in corroborating and fine-tuning the model used in lower completion design of maximum reservoir contact wells in future field development. Along with well performance and real-time surveillance, production/injection logging data demonstrates effective stimulation of the entire lateral.
 This paper presents field performance results from successful bullhead stimulation of extended reach horizontal well completed with LEL in low-permeability-reservoir. This paper also presents our first application of fiber-optic-DTS-DAS real-time-surveillance during stimulation and post-stimulation water injection. Advanced surveillance data demonstrated the success and effectiveness of the LEL completion and stimulation in extended-reach long horizontal open hole laterals.

Bullhead Stimulation and First Real-Time Fiber-Optic Surveillance in Extended-Reach Horizontal Laterals to Maximize Reservoir Recovery in a Giant Offshore Carbonate Oil Field Abu Dhabi

Yasser Ali

Papers

Advanced ERD Lower Completion Technology Performance Update in a Giant Offshore Field UAE

Bullhead Stimulation and First Real-Time Fiber-Optic Surveillance in Extended-Reach Horizontal Laterals to Maximize Reservoir Recovery in a Giant Offshore Carbonate Oil Field Abu Dhabi

A Robust Production Engineering Strategy for Extended Reach Well for Sustained Performance

Strategic Engineering Application for Long Lateral Wells

Robust Completion and Stimulation Design Methodology to Maximize Well Performance for Long Horizontal Laterals in a Giant Off-Shore Field Development