A Review of Completions and Gravel-Pack Techniques of the Xijiang Development
- J.T. Rodgers (Phillips China Inc.) | J.S. Bennett (Halliburton Energy Services) | Tommy Grigsby (Halliburton Energy Services) | Y.K. Zhang (China Natl. Offshore Oil Corp.) | Y.J. Yang (China Natl. Offshore Oil Corp.)
- Document ID
- Society of Petroleum Engineers
- SPE Drilling & Completion
- Publication Date
- December 1997
- Document Type
- Journal Paper
- 249 - 255
- 1997. Society of Petroleum Engineers
- 3.2.4 Acidising, 2.4.5 Gravel pack design & evaluation, 5.1.1 Exploration, Development, Structural Geology, 4.6 Natural Gas, 3 Production and Well Operations, 2.2.2 Perforating, 1.6 Drilling Operations, 2.2.3 Fluid Loss Control, 3.1.2 Electric Submersible Pumps, 2.7.1 Completion Fluids, 4.3.4 Scale, 2.4.3 Sand/Solids Control, 2 Well Completion, 4.2.3 Materials and Corrosion, 4.1.5 Processing Equipment, 5.4.10 Microbial Methods, 5.6.4 Drillstem/Well Testing, 3.2.3 Hydraulic Fracturing Design, Implementation and Optimisation, 4.3.1 Hydrates, 1.14 Casing and Cementing, 4.1.2 Separation and Treating, 1.10 Drilling Equipment, 1.7.5 Well Control, 1.8 Formation Damage
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The first gravel-packed completions have been run in the Pearl River mouth basin of the South China Sea in the Xijiang fields. The reservoirs in these fields are characterized by unconsolidated, friable, high-permeability sandstones, and, as such, presented many challenges. This paper addresses the development of these fields and how reservoir characteristics and parameters and unexpected deviations were experienced by the operator, as well as the impact these deviations had on completion designs.
Important considerations included the need for sand control, zonal isolation, high-rate production, and reduced completion durations. Finally, the practical application and evaluation of pregravel-pack stimulation techniques, gravel-pack carrier consideration, fluid-loss controls, and general completion procedures are presented, along with the innovative completion designs developed to manage these needs.
The Xijiang fields are comprised of numerous stacked reservoirs, many of them containing independent water aquifers that require mechanical isolation. Production is accomplished through use of high-horsepower electric submersible pumps (ESP's). In these fields, operational parameters must address high fluid flow rates, ESP durability, eventual excessive water cuts, lack of sandstone consolidation, and minimal sand-grain cementation; therefore, all wells must be gravel packed.
A major objective was to complete each well with minimal reservoir damage so that maximum well productivity and well control would not be compromised. The following practices were employed to facilitate this goal.
Efforts were directed toward achieving clean completion fluid, acid, and gels throughout the completion.
Underbalanced-tubing-conveyed perforating techniques were practiced that employed large guns followed by a cleanup flow period.
Pregravel-pack stimulation and gravel-carrying techniques were designed to maximize completion efficiency.
Fluid-loss-control treatments (FLCT) were pumped to restrict excessive formation loss after perforating and gravel-packing operations.
Several new completion systems were developed to address conditions specific to the Xijiang area. As of the initial writing of this paper, seven wells [one with conventional stack pack; one with single gravel pack; and five with single-trip, dual-zone (STDZ) gravel packs] had been completed on the 24-3 platform. The STDZ system allows two zones to be gravel packed with a single trip into the wellbore.
The Xijiang project involved the development of two fields, Block 15/11 containing Field 24-3 and Block 15/22 containing Field 30-2. Both fields lie 80 miles southeast of Hong Kong in the Pearl River mouth basin of the South China Sea. Water depth is 100 m. The 24-3 platform was installed in mid-1994, with production beginning in November 1994. The 30-2 platform was installed in the second quarter of 1995 with production scheduled to start in the fourth quarter. Each platform was designed for 16 wells. An integrated drilling rig on each platform drills, completes, and performs workovers on existing wells, which produce simultaneously. Both platforms transport fluid to a floating production and storage offloading vessel, where oil is collected by tanker ships.
Xijiang 24-3 and 30-2 reservoir structures contain 7 to 15 productive sands with separate oil/water contacts. The fields are comprised of multiple-layered reservoirs that must be commingled for production. Productive intervals range from 1830- to 2750-m true vertical depths. Individual sands have porosities ranging from 11 to 30% and associated permeabilities from 500 to 30,000 md. Well deviations range from 20 to 45°, exhibit mild build, and hold well paths to total depth. Maximum reservoir temperatures vary from 97 to 127°C.
Both fields contain a dead oil, with gas/oil ratios of less than 20 scf/STB. Oil gravity ranges from 26 to 38°API and viscosity ranges from 1 to 11 cp. The crude has high wax content ranging from 40 to 50%, with associated high pour points of 32 to 43°C. At reservoir conditions, the fluid contains zero H2S and 0.08 to 1.6 mol% CO2. At surface conditions, the flash gas contains 9 to 40% CO2. Reservoirs are normally pressured with gradients of 1.44 psi/m (0.44 psi/ft).
Most wellbores contain commingled reservoirs to achieve economical flowrates. Reservoirs contain different aquifers and varying rates of water influx. Although commingled in the production tubing, mechanical isolation of the sands with packers (where spacing permits) was needed. Commingled completion intervals can have from two to five separate sands requiring packer isolation within one wellbore. On the basis of individual production characteristics, isolated sands were to be closed by sliding-sleeve circulating devices or nipple profiles upon excessive water influx. Facility water handling or ESP operating limits would traditionally dictate zone closures.
The requirement for clean, filtered completion fluids is of utmost importance in a gravel-packed completion. Fluid that contains solids has the potential to plug the perforation tunnels before gravel placement. Solids either will be hydraulically forced into the formation, causing damage, or will intermix with gravel, creating zones of impairment in the gravel pack.1 Damage caused by undissolved solids can never be totally removed, but can be reduced with proper filtration methods. The high permeabilities at Xijiang are especially conducive to extreme fluid losses. This situation heightens the importance of having clean brine to reduce damage from losses.
A 3% KCl and seawater mixture, resulting in an 8.7-lbm/gal system, was used initially as a compatible completion fluid. After experiencing bottomhole pressure (BHP) decline, 2% KCl was used, yielding an 8.5- to 8.6-lbm/gal system. Overbalances of less than 100 psi had been achieved on earlier wells, with the incremental difference increasing as development progressed.2
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