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SPE 116261 Development of an Expandable Liner Hanger With Increased Annular Flow Area Tance Jackson and Brock Watson, Halliburton, and Larry Moran, Conoco Phillips Company Copyright 2008, Society of Petroleum Engineers This paper was prepared for presentation at the 2008 SPE Annual Technical Conference and Exhibition held in Denver, Colorado, USA, 2124 September 2008. This paper was selected for presentation by an SPE program committee following review of information contained in an abstract submitted by the author(s). Contents of the paper have not been reviewed by the Society of Petroleum Engineers and are subject to correction by the author(s). The material does not necessarily reflect any position of the Society of Petroleum Engineers, its officers, or members. Electronic reproduction, distribution, or storage of any part of this paper without the written consent of the Society of Petroleum Engineers is prohibited. Permission to reproduce in print is restricted to an abstract of not more than 300 words; illustrations may not be copied. The abstract must contain conspicuous acknowledgment of SPE copyright. Abstract Several criteria are important for a cementing operation as it relates to effective zonal isolation. First of all, studies have shown that cementing operations can be improved by rotating and reciprocating the liner. In addition, it has been shown that increased flow rates (prior to cementing, during cementing, and during displacement) can improve zonal isolation. While currently available expandable liner hanger technology can achieve the required liner movement, rotation, and reciprocation to affect a good cement job, these capabilities alone have not been capable of always meeting cementing needs in every scenario. When expandable liner hangers were introduced to the oilfield, they were immediately accepted. Experience has shown that increasing flow rates (prior to cementing, during cementing, and during displacement) can offer improved zonal isolation. A new liner hanger was designed to increase the annular flow area, subsequently reducing annular friction pressure to allow higher flow rates. The added bypass area would also provide reduced surge to the formation while running the liner. This would shorten liner installation times. In addition, by increasing the bypass area, the possibility of solids bridging at the liner hanger (which can cause loss of circulation during circulating and cementing) would also be reduced. When loss of circulation occurs, proper cement placement is jeopardized. This paper highlights the development of the new smaller-outside-diameter (OD) expandable liner hanger. This project was commenced; the new liner hanger has a pre-expansion maximum outside diameter that is smaller than the outside diameter of conventional liner hangers tie-back receptacles and integral top-set packers. The new smaller diameter expandable liner hanger maintains the desirable features of existing expandable liner hanger. Computer modeling including Finite Element Modeling (FEA) will show the design analysis for the expandable liner hanger. Additionally, prototype testing will be performed to validate the new design. The new expandable liner hanger design offers the capabilities to rotate and reciprocate during circulating/cementing and displacing; a simple, robust design for installation reliability; and gas-tight liner-top sealing. Introduction An operator in the North Sea had been experiencing issues with zonal isolation due to poor quality cement jobs. The wells had been drilled into depleted reservoirs where the fracture gradients were very close to the formation pressures. One method sometimes used to increase the quality of the cement job is to increase the circulation rate during clean-up and cement placement. Because of the flow restrictions caused by the liner hangers in currently available designs, an increase in circulation rate would not be possible for this particular application without exceeding the fracture gradient in the well. To meet the needs of this project, the operator and service/engineering personnel felt that a new liner hanger that would allow increased circulation rates was needed. A review of the available liner hangers determined that the expandable liner hanger offered the cleanest flow path in its current design as well as it had the simplest design to modify. This provided a starting point for development of an expandable liner hanger that would address the operators issues in this field development. Since it was recognized that this need was global, the new liner hanger would have application well beyond the North Sea projects, and thus, the design project was initiated. Liner hangers used to deploy and anchor the liner typically are larger in outside diameter (OD) than the liner being deployed. As such, they cause a restriction in the flow path during well circulation and cement placement. Analyses have shown that by decreasing the OD of the liner, even by a small amount, greater circulation rates, and thus, an improved cementing process can be achieved. However, there would be many issues from reducing the OD of the liner hanger that 2 SPE 116261 would require resolution. These issues included reduced strength (pressure rating, tensile rating), the need to reduce the inside diameter (ID) to less than the liner ID, and the elimination of the tie-back receptacle (TBR) from the assembly. There would be added benefits, however, which would include: 1) an increase in liner running speed and the associated time and money saved, 2) fewer instances of loss of circulation during the liner running and cementing process and the associated money saved by preventing drilling fluid losses, s, and 3) increased flow rates with improved zonal isolation and improved production. Zonal Isolation Zonal isolation is critical in the construction of oil and gas producing wells. Cement placement is important to prevent produced fluid migration, support the production liner and provide an annular barrier between the formation and surface1. There are eight basic factors which must be considered if a successful cement job is to be achieved. These factors are summarized as follows: 1. Simulate the job to be performed. 2. Design and test the cement composition. 3. Condition the drilling fluid 4. Properly utilize spacers and flushes 5. Move the liner 6. Centralize the liner 7. Maximize the displacement rate 8. Execute the job as planned. All of these factors can be achieved. However, the ability to maximize the displacement rate has been limited with regard to liner installations using current liner-hanger designs, since the capability to increase circulation rates requires a reduced- OD liner hanger to control ECD within an acceptable range. There are three possible flow regimes in which a non-Newtonian fluid, such as drilling fluid or cement slurry, may exist; i.e., turbulent, laminar and plug.2 Figure 1 illustrates the flow regimes. The dashed lines represent bulk annular velocity, and the solid lines represent the actual velocity in the annulus. Figure 2 illustrates the relationship between turbulent flow and displacement efficiency. High-rate flow in the liner- formation annulus is effective for good mud displacement with turbulent flow around the entire liner most desirable. In many cases, turbulent flow is not a viable option for the wellbore configuration or formation. The best results are obtained when the spacer and cement are pumped with the maximum flow rate. Figure 1 Annular fluid profiles for non-Newtonian fluids. SPE 116261 3 Comparison of Conventional and Expandable Liner Hangers In conventional liner systems, “cone and slip” technology is used to anchor the liner to the previous casing. To accommodate the slip-and-cone mechanism and to provide the strength required to support the liner, a large portion of the available wall thickness is consumed in the liner-hanger design. This creates a difficult design problem when attempting to reduce the assembly OD. Conventional liner hangers are also available with integral liner-top packers that provide isolation between the formation and surface in addition to the primary cement. The elements on this type of packer can be assembled onto the liner- hanger body and secured mechanically. This type of element design can be washed off at high flow rates. The expandable liner-hanger system was developed using expandable solid liner technology with proven cementing products and service capabilities.3,4,5,6 The system uses an expandable liner-hanger body with an integral packer, a tieback polished-bore receptacle, a setting-sleeve assembly, and a crossover sub to connect the assembly to the liner. Elastomeric elements are bonded onto the hanger body. As the hanger body is expanded, the elastomeric elements are compressed in the annular space. This eliminates the liner hanger/casing annulus and delivers liner-top pressure integrity as well as impressive tensile and compressive load capacity. Figure 3 shows a comparison of the conventional and expandable liner hangers. The following features were incorporated into the expandable liner hanger system to address the problems experienced with the traditional systems: 1. Liner hanger and liner-top isolation packers are packaged as a single unit 2. The packer element design allows for high-circulation rates 3. Bonded elements prevent washing at high-circulation rates 4. The fluid-flow bypass has been improved by the elimination of external components such as slips, hydraulic cylinders, cages, etc. 5. Supporting casing sustains less induced stress and greater stress distribution for a given liner length 6. The new design prevents physical damage to the support casing 7. No slip “wickers” to cut into the supporting casing 8. Hanger/packer actuating systems are contained in the setting tool assembly, minimizing the wall thickness required for the actual liner hanger. LAMINAR FLOW TURBULANT FLOW (VELOCITY)2 /MUD IMMOBILITY FACTOR PERCENT MUD RECOVERED 100 80 60 40 20 0 100101102103104 Figure 2 Effect of flow regime on the displacement efficiency 4 SPE 116261 Components Original Expandable Liner Hanger/Packer System The first expandable liner-hanger/packer system incorporated the expandable liner-hanger body with an integral packer, a tieback polished-bore receptacle, setting-sleeve assembly, and a crossover sub to connect the assembly to the liner. The liner-hanger packer is manufactured from materials meeting critical specifications for maximum expandability and performance. The hanger incorporates bonded Viton elastomeric sections for high- temperature and performance requirements. Other elastomers can also be used if Viton is not suitable for the particular wellbore conditions that will be addressed in the application. The elastomers supply both sealing and hanging capability for the liner hanger. A single one-ft elastomer section on the 79-5/8-in. expandable hanger is capable of supporting 500,000 lbf of hang weight. The expandable liner hanger in size 7x9-5/8-in. and larger incorporates five of these elastomeric sections. A single one-ft elastomer section on the 5-1/27-5/8-in. expandable hanger is capable of supporting 350,000 lbf of hang weight. The expandable liner hanger in sizes 5-1/27-5/8-in. or smaller incorporates three of these elastomeric sections. Figure 4 is an expandable liner-hanger system. Figure 3 Comparison of Conventional and Original Expandable Liner Hanger. Handling Pup Rupture Discs Bypass Expansion Cone Expansion Bypass Running Collet Mechanism Force Multiplier Piston Tie Back PBRHangerCrossover Running Sleeve7? Liner Float CollarFloat Shoe Ball SeatContingency Shear Release Wiper Plug Figure 4 Typical Original Expandable Liner Hanger System SPE 116261 5 The Original Expandable Liner Hanger Body The expandable liner-hanger packer body contains no setting mechanism or external components such as slips, hydraulic cylinders, or pistons. Since the hydraulic setting mechanism is contained in the setting tool assembly, it is retrieved. This feature eliminates potential leak paths in the flow stream. The liner can be rotated and reciprocated while running in the hole or during cementing operations as required. However, the hanger cannot be rotated after setting as the elastomeric sections are expanded and will not allow any movement of the hanger at that point. These features led to the decision to use the expandable liner hanger as the base tool to develop a reduced-OD hanger to improve cementing performance. Flowand-Surge Analysis in Cementing Operations The most critical time to consider pressure drop across the hanger is during the circulation and cementing operations. The hanger will be surrounded by drilling fluid except for the last few barrels, when it will be surrounded by cement. Pressure drop around the liner hanger also should be considered for the period of time during installation. The hanger will usually be passing through drilling fluid that has been static for some period of time. Therefore, to perform a Computational Fluid Dynamics (CFD)7 analysis of both circulation friction drop and liner lowering friction drop, highly viscous drilling fluids were selected. The three fluids selected are Bingham model fluids. See Table 1 for the actual fluid properties used for the analysis. The hydraulic calculations were performed on both the old and new system to predict the restriction of fluid in the annulus between the hanger and casing ID. The new hanger has approximately twice the annular flow area of the conventional expandable hanger. It was expected that the pressure drop across the new hanger system while running or circulating would be greatly reduced. CFD modeling was used to calculate pressure drop across an original expandable liner hanger and the reduced-OD expandable hanger. The effect of the increased flow area was found to be a reduction of approximately 90% in pressure drop for the Bingham fluids. Figure 5 shows a comparison of the pressure drop of the conventional expandable liner hanger and the reduced-OD expandable hanger at various flow rates using viscous drilling fluids of various densities. Figure 6 shows a comparison of the pressure drop of the original expandable liner hanger and the reduced OD expandable hanger at various running-speed rates using viscous drilling fluids of various densities. CFD also was used to analyze the surge characteristics of the liner hanger while running into the hole. The results were almost identical to the cementing operation as the pressure drop caused by the surge was reduced by approximately 90%. Figures 5 and 6 demonstrate the substantial effect of the increased flow area with respect to pressure drop across the liner hanger. Any pressure increase due to the liner hangers flow reductions could be significant, depending upon the size of the pore pressure and fracture gradient window. One can see that it is easily possible to obtain 500 psi or more of pressure drop across the original expandable liner hanger (similar pressure drops would be expected for conventional liner hangers since the OD of the liner top packer and tie back receptacle are similar). 500 psi of pressure increase at 15,000-ft of true vertical depth would give an increase of approximately 0.64 ppg of equivalent circulating density, or 1 ppg at 10,000-ft, or 2 ppg at 5000-ft, etc. Table 1. - Drilling Fluid Viscosity Density (ppg) PV (cps) YP (lb/100 sq ft) 9 39 23 13 54 34 17 105 72 6 SPE 116261 Figure 6 Calculated pressure drops across the liner hanger while running the liner into the well comparing the original tool design and the improved design with different fluid densities inside of an 8.535-in.-ID casing. Figure 5 Calculated pressure drops across the liner hanger comparing the original tool design and the improved design with different fluid weights. Low ECD 8.100 (9 ppg) Low ECD 8.100 (13 ppg) Low ECD 8.100 (17 ppg) Standard 8.310 (9 ppg) Standard 8.310 (13 ppg) Standard 8.310 (17 ppg) 1400 1200 1000 800 600 400 200 0 01234567 Circulating Rate (bbl/min) Pressure Drop (psi) Circulating Pressure Drop Across Hanger Low ECD 8.100 (9 ppg) Low ECD 8.100 (13 ppg) Low ECD 8.100 (17 ppg) Standard 8.310 (9 ppg) Standard 8.310 (13 ppg) Standard 8.310 (17 ppg) 1400 1200 1000 800 600 400 200 0 020406080100120 Running Speed (ft/min) Pressure Drop (psi) Running Pressure Drop Across Hanger 1600 SPE 116261 7 Development of the Reduced-OD Liner Hanger Flow analysis shows that an OD reduction of 0.20 inches will allow for a dramatic increase in flow rate for a given pressure drop across the liner hanger. 9 5/8-in. 53.5 lb/ft casing typically has an ID of 8.535-in. The original expandable liner hanger designed for 9 5/8-in. 53.5 lb/ft casing has an OD of 8.310-in. This gives an annular clearance of 0.1125-in. By reducing the OD of the liner hanger to 8.100-in. the annular clearance is increased to 0.2175-in. This may not seem like a large change but it must be remembered than annular friction pressure is reduced exponentially and not linearly when the OD of the inner pipe is reduced. Another important point to remember is that with an increased annular clearance from approximately 0.1-in. to 0.2-in. the potential for annular bridging by solids left in the well is greatly reduced. It will take cuttings with a diameter of nearly 1/4-in. to bridge the annular gap vs. cuttings with a diameter of 1/8-in. to bridge the original liner hanger annular gap. Being capable of rotating and reciprocating the liner hanger while circulating also greatly increases its capability to pass solids by the liner hanger. In order to achieve this reduction in OD, new design parameters had to be established. Design criteria were established to meet the end users