DEEPWATER COMPLETIONS TECHNOLOGY.

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1 DEEPWATER COMPLETIONS TECHNOLOGY. Bruce Dale, Darren Rosenbaum, Scott Clingman, Marcus Asmann ExxonMobil Upstream Research Company Copyright 25, CIPM. Este artículo fue preparado para su presentación en el cuarto E-Exitep 25, del 2 al 23 de febrero de 25 en Veracruz, Ver., México. El material presentado no refleja necesariamente la opinión del CIPM, su mesa directiva o sus colegiados. El artículo fue seleccionado por un comité técnico con base en un resumen. El contenido total no ha sido revisado por el comité editorial del CIPM. SUMMARY As fields are developed with fewer wells and in more technically challenging deepwater environments, obtaining superior well performance will require new technologies to deliver mechanically robust and reliable wells that can be operated at the high rates required to meet aggressive production targets. To address this challenge, ExxonMobil has developed advanced completion design and well performance modeling capabilities based on fundamental physics to ensure well operability and producibility. These technologies provide the ability to determine the physics-based technical limits for well production, thereby enabling optimization of overall well performance. Deepwater reservoirs are typically composed of unconsolidated sands. As a result, deepwater developments often require wells that are completed with sand control. However, reliable installation of deepwater sand control completions can be challenging. ExxonMobil has developed technologies that provide industry-leading capabilities to reliably install long-interval, highly deviated, openhole gravel pack completions. These technologies, such as alternate path and improved installation techniques, have been utilized extensively to install openhole gravel packs in West Africa. TECHNICAL LIMIT PRODUCTION Ensuring long-term well integrity and optimum completion performance is essential for economic development of deepwater assets. ExxonMobil has developed unique, physics-based modeling capabilities that can be applied during both well planning and production to deliver optimized well performance. The modeling capabilities can be used to address issues typically associated with deepwater developments such as reservoir compaction, sand production, flow impairment and tubular design. The modeling capabilities integrate the underlying fundamental physics to provide a more accurate determination of well performance technical limits. ExxonMobil has developed the capability to quantitatively define a well integrity related technical limit, called a well operability limit, that establishes the boundary between safe well production operations and completion failure due to compaction associated with reservoir depletion and/or drawdown. The well operability limit is determined by detailed finite element analysis. As shown in Figure 1, producing conditions throughout the life of a well can be compared to the well operability limit to assess the current well integrity status. The technology is currently being used for production guidance at an ExxonMobil operated deepwater GOM asset that experienced some early compaction related well failures. By defining the compaction related well operability limit, additional well failures have been avoided. In addition, the well operability limits provided the confidence to produce several wells more aggressively than would have been prudent without the quantified technical limit. Drawdown [psi] Safe Zone Failure Zone Depletion [psi] Figure 1. Well Operability Limit Determination of the potential for sand production early in the planning stages of a deepwater well is essential for selecting the appropriate completion type. Unexpected sand production can result in 1

2 significant revenue loss due to increased maintenance and workover operations, damage to equipment and reduced productivity. ExxonMobil has developed the capability to determine the potential for sand production using core data, log data and finite element analysis. Figure 2 shows an example finite element model used to evaluate the potential for sand failure around a wellbore and perforation. This technology has been applied to many fields to help determine the completion and production options that result in optimum well performance. For example, the technology has been used to determine selective perforation strategies that maximize sand-free production for cased and perforated high-rate gas wells. Figure 2. Finite element model for sand failure analysis. Since understanding the potential for flow impairment is important for predicting or evaluating well performance, ExxonMobil has developed technologies to characterize the impact of drilling, completion and production operations on well productivity. These effects are evaluated through an integrated program of laboratory testing and physics-based numerical modeling. Small and large-scale laboratory flow tests are used to quantify the damaging effects of various impairment mechanisms on gravel packed completions. Figure 3 shows the large-scale wellbore simulator used to conduct these experiments. The test results are integrated with numerical flow and geomechanical models that quantify the impact of completion design on flow impairment and long-term impairment due to reservoir compaction. The ability to characterize flow impairment mechanisms allows more accurate prediction and diagnosis of well performance. Figure 3. Large-scale wellbore simulator for evaluating flow impairment. ExxonMobil uses physics-based approaches to design wells that will be subjected to complex loads encountered during deepwater production. A probabilistic tubular design method, ExxonMobil Load and Resistance Factor Design (EMLRFD), has been used extensively to determine reliable and low cost casing and tubing designs. The method was developed using information obtained from thousands of pipe inspections and load data from hundreds of instrumented drill wells. Detailed flow modeling and multi-string force balances have also been combined with the probabilistic tubular design methods to evaluate and mitigate the effects of, for example, annular pressure buildup and wellhead growth. For tubular connections qualification, ExxonMobil's Connection Evaluation Program combines non-linear finite element analysis with full scale physical testing. Rigorous physical tests include make-and-break, gas sealability, structural failure, internal quench, collapse and thermal cycle tests. The final result of the rigorous computer modeling and physical testing is a performance envelope that defines the operational limits for the tubular connection in actual field applications. Figure 4 shows the various components of the Connections Evaluation Program. 2

3 Net Pressure Load (psi) 1 5 Industry Leading Computer Analysis Connection Performance Envelope Liquid Seal Only Gas and Liquid Seal Pipe Yield -5 Ellipse Manufacturer's Rating Axial Load (kips) Industry Leading Physical Test Facility acidizing treatment was placed using coiled tubing on a floating production platform and pumped from a marine stimulation vessel. As shown in Figure 5, the stimulation treatment dramatically improved productivity. Production logs prior to and following the stimulation treatment were essential for evaluating well performance and treatment effectiveness. 16, Results Production: 4k to 12k bopd Drawdown: 1 to 214 psi PI increased from 4 to 6 Oil Rate (bbls/day) 12, 8, 4, Drawdown (psi) Dec- Feb-1 Apr-1 Jun-1 Aug-1 Oil Rate Oct-1 Dec-1 Feb-2 Drawdown Apr-2 Jun-2 Computer analysis verified with full-scale optical strain mapping Figure 4. Connection Evaluation Program. The modeling capabilities described above integrate the necessary underlying fundamental physics such as geomechanics, fluid mechanics and well mechanics. This integration enables a more accurate determination of well performance technical limits. With the technical limits quantitatively defined, wells can be appropriately operated to achieve superior performance. As wells are increasingly instrumented with downhole gauges, the availability of downhole data provides an opportunity to improve well performance. As a result, ExxonMobil has also developed tools that enable efficient processing and analysis of continuous downhole gauge data. During production operations, the modeling capabilities previously described can be used in conjunction with downhole data to diagnose well performance. For example, Figure 5 shows the production history of a deepwater GOM well completed with a long interval, high angle openhole gravel pack. 1 Monitoring of continuous production data for this well indicated a steady decrease in well productivity. Detailed analysis of the downhole gauge and production log data was conducted to identify the flow impairment mechanism responsible for the productivity decrease and was used to design an appropriate remedial stimulation treatment. A sandstone Figure 5. Well productivity pre- and post-stimulation. RELIABLE INSTALLATION OF DEEPWATER OPENHOLE GRAVEL PACK COMPLETIONS Deepwater reservoirs are often composed of unconsolidated sands and as a result are typically developed with wells that are completed with sand control. Various options are currently utilized for wells that require sand control completions such as openhole gravel packs. A properly designed openhole gravel pack can deliver high production rates while maintaining reliable, long-term sand control. However, installation of these completions for long, openhole intervals at high angles can be challenging. Maintaining hole stability during installation and placing gravel throughout the entire completion interval are imperative. To overcome these challenges, ExxonMobil has developed distinguishing technologies involving improved techniques and completion hardware that provide industry-leading capabilities to reliably install high rate, long interval, highly deviated, openhole gravel pack completions. These technologies have been utilized extensively to successfully install openhole gravel packs in deepwater West Africa. For deepwater wells that require sand control, nonaqueous fluids are often preferred for improved performance during drilling operations. If an openhole gravel pack is the sand control completion of choice, conventional installation techniques typically involve displacing the nonaqueous fluid from the openhole interval prior to running sand control screens to depth in the 3

4 wellbore. An aqueous fluid is used for the displacement since subsequent gravel packing of the openhole interval is conducted using a water based fluid. Maintaining hole stability during the displacement and running of sand screens can be problematic since exposed shales may be sensitive to the aqueous fluids. Several deepwater developments have experienced problems when attempting to run sand screens using the conventional techniques. As a result, operators for several developments have resorted to installing predrilled liners as a conduit for running screens or have chosen to install alternative sand control completion types that provide less reliable sand control. Instead of settling for these options, ExxonMobil developed a novel technique that enables reliable installation of long interval, highly deviated, openhole gravel pack completions. 2 The ExxonMobil developed installation technique involves running sand screens to depth in nonaqueous fluid followed directly by displacement and gravel packing using an aqueous, viscous fluid. Prior to running screens, the nonaqueous fluid is conditioned, or filtered, to remove solids that may cause screen plugging. The practice of running sand screens in conditioned nonaqueous fluid is commonly utilized for non-gravel packed, stand alone screen completions and provides an extremely reliable method for screen installation. But for a gravel packed well, the conditioned, yet still solids laden, nonaqueous fluid must be displaced from the openhole interval with sand screens already installed. To address the various concerns that were identified, rigorous lab and field-scale tests were conducted to verify that the technique was viable. In addition, required operational procedures and service tool modifications were identified and implemented to enable application of the installation technique in the field. This installation technique is preferably conducted utilizing alternate path technology described in the following paragraphs. Once sand screens have been successfully run to total depth in the wellbore, the next major objective is to completely pack the openhole interval with gravel. Conventional techniques such as circulating water packs for placing gravel in the annular space between the sand control screen and the formation face are often compromised by sand bridges that prematurely form in the annulus. The sand bridges obstruct gravel slurry from being circulated throughout the entire openhole interval and prevent gravel placement in the annulus below the bridge. Without a complete pack, the sand control integrity of the completion may be compromised. As a result, ExxonMobil developed alternate path technology since the potential for premature sand bridge formation is significant for long interval, high angle wells that are completed through intervals with reactive shales. Alternate path technology involves alternative flow conduits, or shunt tubes, that are mounted on the exterior of the sand control screen. The shunt tubes allow gravel slurry to bypass sand bridges that prematurely form in the annulus. If a sand bridge is encountered during a gravel packing operation that utilizes alternate path technology, the gravel slurry will eventually be diverted into the shunt tube and consequently circulated below the bridge that blocks the annulus. Figure 6 shows gravel slurry diverting down the shunt tubes in order to pack void space in the annulus beyond a fracture induced bridge. Outlet ports, or nozzles, that are positioned along the length of the shunt tube allow the gravel slurry to exit the shunt and continue packing the openhole interval below the bridge. Ultimately, all voids in the pack will be filled with gravel. Alternate path is an ExxonMobil patented and licensed technology. 3,4 Figure 6. Alternate path gravel packing technology. The combination of improved operational procedures and alternate path technology has been 1% successful (27 out of 27) to date in ExxonMobil operated deepwater West Africa wells. For all wells, sand control screens were successfully run to total depth and the openhole intervals of up to 25-feet were completely packed without the use of a predrilled liner. In addition, the operations were conducted using less rig time than conventional openhole gravel packing techniques. Most importantly, initial flow tests for these wells have consistently indicated highly flow efficient completions that are capable of delivering the expected production rates. 4

5 REFERENCES 1. Hardin, F. Lee, Barry, Mike D., Shuchart, Chris E., Gdanski, Rick D., Ritter, D. Wes and Huynh, David V.: "Sandstone Acidizing Treatment of a Horizontal Openhole Completion Using Coiled Tubing From a Deepwater Floating Production Platform", paper SPE presented at the SPE Annual Technical Conference and Exhibition held in Denver, Colorado, U.S.A., October Hecker, Michael T., Barry, Michael D. and Martin Jr., Thomas B.: "Reducing Well Cost by Gravel Packing in Nonaqueous Fluid", paper SPE 9758 presented at the SPE Annual Technical Conference and Exhibition held in Houston, Texas, U.S.A., September Jones, L. J.: U.S. Patent No. 4,945,991 (August 7, 199). 4. Jones, L. J. and Yeh, C. S.: U.S. Patent No. 5,113,935 (May 19, 1992). 5