Search

Optimization of permanent liner completions in the North Kuwait Jurassic Gas (NKJG) reservoirs has been an ongoing challenge progressed on a steep learning curve within the last decade. Various completion options are field-tested in determining the optimal completion hardware and activation methodology. The asset's objectives have been multi-dimensional: preserve natural fractures, minimize formation damage, segregate, stimulate and activate optimally, while installing permanent completions hardware efficiently, which can withstand 15,000-psi differential pressure at high temperature and sour gas environment and sustain production for the well life of over 20 years.NKJG faces the enormous task of increasing the hydrocarbon production potential by over 200% within a short time period. The reservoirs are high-pressured and high-temperature (HTHP) gas condensate assets with tight matrix properties (i.e. Custom-designed multi-stage completion assembly (MSC-HP) was successfully installed, sequentially hydraulic-fracced and commingle-tested on flowback. Customized operational guidelines were established including a pre-set success criterion, openhole and caliper log sequences, tie-back cementation and subsequent clean out trips, followed by hole conditioning and reamer runs to compute the final drag and friction forces. Differential sticking risks were mitigated by avoiding the "pressure ramps" exacerbated by differential depletion evident in the area. Reservoir was segmented in three distinct intervals to maximize flow potential. As a result, the asset's objectives were successfully met, with the additional benefits of proving multiple zone activation, each with a complicated sequence of operational events, performed sequentially in four days.This paper documents the project cycle from successful planning and design, to installation and execution phases of the MSC-HP in peripheral deep NKJG asset. Key learnings and critical factors, which led to the successful well results in spite of less favorable subsurface location are summarized. Added complications due to the severe NKJG specs will be discussed as the number of global analogues is scarce leading to limited opportunities for the industry to learn from in unconventional/conventional mix layered carbonates.

The HPHT, sour, deep, fractured and not so fractured carbonate Jurassic formations within the North Kuwait cluster of fields present extraordinary challenges in driving towards an optimized field development that maximizes liquid recovery and meet the gas production aspirations for the state of Kuwait. The Middle Marrat reservoir has been developed to date with cased and perforated liner completions across the 500- 700ft pay. However due to the high permeability contrast between the different reservoir flow units, the low permeability zones are typically not contributing. This is further exasperated with the inability to effectively acid stimulate large proportion of the net pay with a single stage bullhead treatment especially when the contrast in permeability between the various flow units is higher than one order of magnitude. Key to successful reservoir management of the Middle Marrat whilst maximizing well capacity to meet the production aspirations is to implement a completion and stimulation strategy that maximizes flow contribution from as much of the net pay as possible. Single stage bullhead matrix acid stimulation treatments like those executed in the past will only stimulate the top decade of permeability. The current 4-1/2" cemented completion ‘plug and perf’ standard will require intensive well intervention to set and drill out plugs in order to selectively stimulate individual zones. To develop an alternative completion and stimulation strategy for developing Middle Marrat, the first 4-1/2" multistage ball activated sleeve completion system has been deployed successfully in a Middle Marrat deviated development well. 2 out of 3 stages installed have been acid stimulated and flow tested showing excellent results. The operational experience and learnings acquired from the project have provided the necessary confidence to the organization to deploy the technology in tight gas and unconventional reservoirs within North Kuwait, but also challenge the existing cemented ‘plug & perf’ completion and stimulation approach for the development of the more conventional Middle Marrat reservoirs.

Objectives/Scope Unconventional organic-rich carbonaceous shale (OCS) in North Kuwait has unique characteristics due to its high total organic content (12–14%), its complex mineralogy (blend of carbonates and clastics) and Jurassic/post-Jurassic complex burial and tectonic history. The OCS is under/over-laid by tight carbonates, where the system permeability is in the range of nano to micro-Darcy. Conventional techniques to initiate flow from this complex reservoir have proven ineffective, which led the appraisal team to develop novel and extensive workflows to characterize the formation properties for successful hydraulic fracturing and to determine the commercial flow potential of hydrocarbons. Methods, Procedures, Process Three vertical wells were identified as the high potential candidates in the appraisal program, prior to the completion of horizontals in this complex formation. A comprehensive logging suite was acquired which included spectroscopy, sonic and image logs. Fracture pressure analysis was performed on an offset well followed by exhaustive diagnostic tests using both non-viscous and viscous fluids. Bottom hole gauges were hanged in the well during the diagnostic tests as well as temperature logging was performed after the diagnostic pumping to define fracture height growth/containment. Proppant fracturing in these wells are planned using nonradioactive tracer proppant. Results, Observations, Conclusions Maximum clay content in the OCS is estimated close to 40% in addition to the high organic content. Anisotropic mechanical earth model was built using sonic log response for fracture modelling in planar 3-D simulators. Some open fractures were observed from the image logs. Fracture pressure analysis on the offset well confirmed “fraccability” of the OCS within the allowable pressure limits. Analysis of the diagnostic tests confirmed significant impact of natural fracture on hydraulic fracture propagation. Nolte-Smith plot using actual bottom-hole pressure revealed very high net pressure slope during viscous fluid stages that raised significant concerns on possibility of placing proppant. Interventions after the diagnostic tests showed flowback of formation material in the form of “formation creep” into the wellbore and that lead to concerns on formation integrity and risks in proppant placement. Novel/Additive Information This paper discusses various methods used to understand the complex OCS formation and integrates extensive analysis achieved through different methods. Interpretation of this data-set and building a model which will be used for development of future horizontal wells will also be presented. It is believed that the inherent challenges presented by the OCS are unique without any true global analogues in the unconventional gas and oil programs.

Appraisal program of the deep gas/light oil from unconventional reservoirs in North Kuwait is strategically important to secure the challenging hydrocarbon production targets of Kuwait Oil Company (KOC). A very deep high-temperature/high pressure (HT/HP) dolomitic formation is at approximately 15, 000 ft (vertical), poses complex completion and producibility challenges. Exhaustive log suite and core analyses confirm some porosity development and gas shows. Unlike the proven carbonates up-hole in the same asset, the deepest dolomite units have extremely low permeability, and may not flow unless enhanced by a natural fissure network and/or hydraulic fracturing. Only a few wells have been attempted for completion in these deepest dolomite layers, which failed to flow even after matrix acidizing treatments. The effective completion design will require good understanding of formation mechanical properties and fluid leakoff behavior, leading to optimal horizontal wells to maximize reservoir exposure completed with multiple hydraulic fracturing treatments to establish hydrocarbon production at commercially acceptable rates. Therefore, properly designed and effectively executed extensive fracture diagnostic tests are critical in the current pre-appraisal stage. In addition, multiple acid-fracturing treatments have already contributed to the understanding of fracture geometry development and fracture flowback characteristics. A fracture diagnostics workflow was developed and deployed to appraise the deepest dolomite layers. Critical fracture mechanics data were collected and analyzed. The main fracturing treatments have also yielded crucial results, which will help the design team in optimizing the horizontal well completions. This comprehensive workflow can be successfully applied in characterizing challenging formations elsewhere where the well and regional data are limited in the appraisal of similar light oil/tight gas-bearing unconventional carbonates.

The Heterogeneity Index (HI) process was utilized in order to demonstrate production gain opportunities in a very short period of time, in a large mature ME field with around 500 wells producing from different reservoirs. The HI process provided a quick screening method of identifying preliminary candidate wells with anomalous behavior (over/under performance) for further analysis and most importantly, provided the foundation for the overall Structure Production Approach. This process; HI, can be calculated by utilizing OFM. A Cross Hair Plot has also been utilized to show the comparison of the HI of two variables in the same plot, creating an easy way to identify wells behaving differently from the average. The cross hair plot can be combined with X-Y Coordinated plot which reproduces the location of the wells. The results from this screening tool were utilized to identify the families of productivity problems at field level, and additional fast screening was done at well level to identify candidates for production enhancement. Representative Wells were selected for detailed diagnostics based on the relevance and size of productivity impact and, the potential of its production rate or well deliverability. Once a few "top potential" wells were identified, production engineering workflows were implemented in order to assess and forecast the potential of production incremental and try to determine and evaluate the best probable action. Some of the key innovate workflows used to complement production enhancement were: Time- lapse nodal analysis (honoring production history and neighboring wells), rate transient analysis (to consume sporadic/low frequency production data), single wellbore modeling (based on logs and flow units), among others. This paper will demonstrate the Production Enhancement Technologies Methodology, in particular the HI process with real examples; pending on data release approval from the owner and the progress of the operations.

The effectiveness of stimulation using hydrochloric acid in high permeability, fractured carbonate reservoir is a challenge due to several reasons like fast acid spending rates, high leak off and non-effective diversion. All these limit the success rate of matrix stimulation using hydrochloric acid. Ultimately the communication between reservoir and wellbore will be less optimum leading to less than expected well performance. The industry is in continuous search of an effective stimulation technique through which good communication between reservoir and wellbore can be established. In the pursuit of maximizing oil production, Kuwait Oil Company is implementing various new technologies. Recently, acid tunneling technology was piloted in an old producer well in one of its prolific yet challenging Mauddud carbonate reservoir. Acid tunneling is a new approach of stimulation that supersedes normal matrix stimulation in carbonate reservoirs to enhance reservoir contact by creating tunnels through dissolution of rock in acid. Mauddud is a super-giant depletion-drive oil reservoir in NK field undergoing massive development efforts with enhancement in oil production through phased pattern-water flood. The reservoir has 10 layers and the average permeability of the reservoir ranges between 15 md to 1D predominantly due to fractures and vugs, which are distributed and extended variedly from layer to the other. The acid tunneling pilot was performed in an old well in Mauddud limestone located in south-eastern part of Raudhatain field where the rock quality is poor compared to the crestal area. The well was selected for pilot due to poor production. The well does not enjoy injection support due to a sealing fault between it and an injector, lying a kilometer away. The well penetrated three layers A, B and C in Mauddud. Two tunnels of 25 ft each were created using 15% HCl acid. The well showed good production after acid tunneling job and the productivity index of the well increased three times. The well is still showing good performance even after one year. These pilot results lead to full scale field implementation of this technology. The paper presents a case study describing advantages of acid tunneling, well selection criteria for this technology application, selection of effective acid concentration for the job and also limitations of the technology. All these informations work as a guideline to implement this technology in mass scale.