Reducing risk and cost offshore Malaysia

November 1, 2011

Combining Alternate Path shunt tube technology with concentric sandface completion systems is improving operational efficiency and economics while bringing new life to old offshore wells in Malaysian waters. Here, Schlumberger's Shahryar Saebi and Sergey Tyutikov and Petronas Carigali's Moustafa ElhusseinySunanda Magna Bela and Zahidi Ibrahim discuss the results. 

Mature offshore Malaysia wells are being worked over as part of a production enhancement program in a depleted, highly unconsolidated, laminated sandstone reservoir. Combining the Schlumberger Alternate Path† gravel pack system, MZ (multizone) packers and the VES (Viscoelastic Surfactant) fluid system for gravel packing has helped to improve operational efficiency and control formation damage to reduce cost and risk while extending field longevity.

The test well for the project initially came online in 1977, producing from the upper zone. A 1979 attempt to test the lower zone was unsuccessful because of sand accumulation above the plug. The upper zone continued to produce at a gradually declining rate until 1980, when a sand clean-out was performed. At that time, new perforations were added to the lower zone, and production was commingled with that from the upper zone. During a three-day test, the zones tested 100% water and were isolated with a blanking plug. Production then resumed from the upper zone but continually declined while water cut increased. When the well in 160ft water depth was plugged in 1995, water cut had increased to 50%.

Petronas recently embarked on a workover program with the following objectives: 1) isolate the lower waterbearing intervals; 2) apply sand control techniques to control sand production; and 3) produce selectively from the lower and upper zones. The project was complicated by threats of substantial losses of completion fluids into the depleted reservoir and by challenges related to gravel packing the lower zones posed by the presence of existing perforations in the upper zones. Additionally, Petronas required selective zonal production capability from the various zones throughout the life of the well.

Three sand control methods standalone screens, expandable sand screens, and cased-hole gravel packs – were considered for the workover program. The three options were evaluated for ensuring successful prevention of sand and fines migration considering formation particle size distribution, productivity index, and reliability and failure rates of each completion method. Gravel packing was determined to perform best against all three criteria and had been used successfully in the field, and so was selected for the program.

Several gravel packing options were considered from technical and economic perspectives. They were assessed according to their ability to meet four particular challenges:

  • gravel packing lower zones in the presence of existing upper zone perforations;
  • selectively producing from various zones over the life of the well;
  • controlling losses to each zone following gravel pack operations;
  • overall cost effectiveness versus conventional methods.

The key contender in addition to the shunt tube technology was a sequential method. First, the existing perforations would be squeezed and sealed off and the lower zone perforated and gravel packed. Then, the completed lower zone would be temporarily plugged while the upper zone was perforated and the wellbore cleaned. Next, the temporary plug would be retrieved and the upper zone gravel packed. By requiring significantly more time and mechanical elements, the sequential method was deemed to pose higher potential risk. A combination of the shunt tube technology and concentric sandface completion technologies was selected. Figure 1 shows comparative completion time between conventional and alternate path gravel packing methods.

Alternate Path technology

The Alternate Path system uses shunt tube technology to bypass annular blocking that can occur during completion operations and to ensure full, uniform gravel placement across long intervals and highly variable formations. Rectangular, stainless steel tubes, or shunt tubes, are welded onto the screens to move the slurry from joint to joint. The tubes have nozzles that allow slurry to exit the tubes into the annulus. When a bridge builds prematurely in the annulus, the shunt tubes become the path of least resistance and the slurry bypasses the bridge, exiting from the shunt wherever a void exists in the annulus. The pack builds in the annulus when the carrier fluid flows through the screen or into the formation (Figure 2) The full, uniform pack prevents formation sand from moving into perforation tunnels and also protects the screens from plugging and erosion associated with fines production. The shunt tube dimensions (0.5in x 1inOD, 0.31in x 0.81inID) and their eccentricity to the body of the screen and blank pipe minimize external diameter.

Proppant suspension capabilities and rheological properties to minimize both gravel settlement during placement and friction pressure in the shunt tubes. Polymeric carrier fluids can cause formation damage because the polymer may enter the formation and be difficult to remove completely. Additionally, the viscosity of polymer-based fluids reduces leakoff into the formation and can negatively impact packing efficiency.

The VES fluid carries the gravel with its suspension capabilities and ensures that the gravel enters the perforations efficiently. Because the fluid carrier mechanism is predominantly based on mechanical carrying capabilities, leakoff is not restricted. During flowback, the fluid breaks completely when it comes in contact with reservoir fluids, so it causes no damage to the formation. With no polymeric residues and complete viscosity loss upon contact with most crude oils, VES fluids exhibit low friction pressure and compatibility with enzyme and chelating agents, giving them high retained-permeability characteristics and making them useful for simultaneous gravel packing and filtercake cleanup.

For the application in Malaysia, the gravel packing fluid used proppant loading of 5lbm/gal added to a VES solution of 6% concentration: the optimum for friction reduction properties and suspension capabilities. Expected friction pressures in the tubes were estimated by considering possible pumping rates during treatment.

Concentric sandface completion

A concentric completion system was selected for the workover project to provide a circulation flow path during gravel placement, ensure fluid loss control after the gravel pack placement, and enable selective production during the life of the well. The basis of the completion system is the MZ multizone packer, a cup-type packer with shunts in the cup/base pipe annulus and no moving parts. Sealbore internal diameters (IDs) make the packer suitable for selectiveproduction completions.

Using the MZ packer, the upper zone is packed conventionally. To pack the lower zone, the slurry is diverted through the shunts and bypasses the packer. At 6ft in length, the packer enables isolation of multiple sand bodies separated by relatively thin shale sections. Conventional stacked completions require minimum 15ft to 20ft spacing.

Placing a tail pipe with a sliding sleeve and isolation seal assembly inside the screen across each zone provides the internal isolation necessary to selectively produce or isolate each zone. This flexible arrangement makes it possible to shut off The carrier fluid for proppant is a non-damaging VES fluid that has strong zones that are producing undesired water or gas. The configuration also enables selective single-zone production.

Completing the target well

Two zones, A and B, were completed in the target well. The zones were gravel packed in one run using the Alternate Path system and a three-way concentric completion system with a 27/8in inner string and sliding sleeve doors for each zone. Polished bore receptacles placed above the multizone packers accommodated the isolation seal assemblies to isolate internally between the inner string and screens.

Figure 3 shows the treatment record. Pumping began at 5bbl/min with 5lbs/gal proppant concentration. The difference between the slurry and wellbore fluid densities caused the treating pressure to decrease with time before the slurry reached the formation. The clear indication of the surface pressure response is evidence that the gravel reached the desired depth and began to be squeezed into the perforations, and that the screen/casing annulus was filling with gravel. As packing of the upper zone neared completion, the shunt tubes were fully activated, and gravel packing the lower zone began. This action was confirmed by an increase in annulus pressure once the proppant reached the lower zone. After the upper and lower zones were filled with gravel, the shunt tubes were packed and treatment screen out occurred. OE

Figure 1: Alternate Path gravel packing requires significantly less time than conventional mehtods, making it less risky and more economical.

Figure 2: The Alternate Path gravel pack system uses shunt tube technology to bypass premature annular blocking and create full, uniform gravel packs across long intervals and higly variable formations.

Figure 3: The simultaneous gravel packing of two zones saved approximately 81/2 days of rig time by eliminating extra trips. The lower number of trips, mechanical packers to be set and temporary plugs to be set and retrieved also reduced operational risk. Ideal packing efficiency in the perforation tunnels and annular space around the screens helped improve production rates and extend completion life.

 

Figure 4: The concentric completion system provided a circulation path during gravel placement, helped control fluid loss after gravel placement, and enabled selective production.


 

Moustafa Elhusseiny is a senior production technologist with Petronas Carigali, based out of Kuala Lumpur, and is the production technologist for the Baram field-RS team and EOR project. He has seven years' oil & gas industry experience – in workover operations, including sand control, production enhancement, field development planning and HSE – and has worked in different locations and environments in Egypt and Malaysia.


 

Zahidi Ibrahim is currently the workover superintendent with Petronas Carigali (PC SB), working out of the Petronas Twin Towers HQ in Kuala Lumpur. With 26 years' oil & gas industry experience in the subsurface area (reservoir engineering, well completion, intervention and workover) with Esso Production Malaysia and PC SB to his credit, his current job scope involves managing a 460kips hydraulic workover unit operating on PC SB's domestic offshore platforms/jackets in east and west Malaysia.

 


 

Sunanda Magna Bela is a workover manager with Petronas Carigali based in KL. He has 12 years' oil & gas industry experience, mainly in stimulation/fracturing, sand control, completion/smart completion and workover & intervention. His current job scope is managing technical & operational, contractual and budgetary issues for two hydraulic workover rigs under the drilling division of PC SB's Well Delivery-Intervention Department.

 


 

Shahryar Saebi is a principal completion engineer with Schlumberger, based in Kuala Lumpur. He has 19 years' experience in the oil & gas industry globally, focused mainly on sand control, acid stimulation/fracturing, coiled tubing/nitrogen, water control and cementing services. He is the leader of Schlumberger's sand management services special interest group.

 


 

Sergey Tyutikov is a technical engineer with Schlumberger, based in Moscow, and is currently the leader for sand control projects in Russia and the Caspian region. He has five years' experience in the oil & gas industry, mostly in the areas of sand control and completion technologies, and has worked in several locations around the world, including the Asia Pacific region and Russia for Schlumberger.



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