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Sand production remains one of the key risks to maintaining field production rates and maximizing ultimate recovery from mature fields offshore Brunei. Due to the operational challenges and the HSE risks resulting from sand production in the surface facilities, sand producing wells are shut-in prematurely, locking-in well production and remaining hydrocarbons. Very fine, poorly sorted formation sands and uncertainty in general about formation sand particle size distribution leads to a challenge in designing robust downhole sand control completions. Sometimes we get it wrong resulting in the failure of the original sand control completion. Low cost options to remediate sand production through the deployment of wireline conveyed thru-tubing standalone screens are typically not reliable in this environment and often considered as a last resort option. In addition most of the existing wells are old, have well integrity problems and completed with small 3-1/2" tubing that limit the application of mechanical thru-tubing options. Expensive rig interventions to workover or redrill sanded out wells are typically not justified by the low remaining reserves. To overcome these challenges Brunei Shell Petroleum embarked on an effort to identify and field test a viable rig-less remedial sand control solution for unlocking production and maximising recovery from existing wells. This paper documents the work done to select the right technology and the right well candidates for a field trial, the design and planning effort that resulted in the first successful application of a Thru-Tubing Gravel Pack (TTGP) in the NW Borneo region. A well previously producing sand has now been producing sand free for about a year. In addition the paper provides valuable learnings to those wishing to deploy thru-tubing gravel packing technology in existing wells.
Sand production remains one of the key risks to maintaining field production rates and maximizing ultimate recovery from mature fields offshore Brunei. Due to the operational challenges and the HSE risks resulting from sand production in the surface facilities, sand producing wells are shut-in prematurely, locking-in well production and remaining hydrocarbons. Very fine, poorly sorted formation sands and uncertainty in general about formation sand particle size distribution leads to a challenge in designing robust downhole sand control completions. Sometimes we get it wrong resulting in the failure of the original sand control completion. Low cost options to remediate sand production through the deployment of wireline conveyed thru-tubing standalone screens are typically not reliable in this environment and often considered as a last resort option. In addition most of the existing wells are old, have well integrity problems and completed with small 3-1/2" tubing that limit the application of mechanical thru-tubing options. Expensive rig interventions to workover or redrill sanded out wells are typically not justified by the low remaining reserves. To overcome these challenges Brunei Shell Petroleum embarked on an effort to identify and field test a viable rig-less remedial sand control solution for unlocking production and maximising recovery from existing wells. This paper documents the work done to select the right technology and the right well candidates for a field trial, the design and planning effort that resulted in the first successful application of a Thru-Tubing Gravel Pack (TTGP) in the NW Borneo region. A well previously producing sand has now been producing sand free for about a year. In addition the paper provides valuable learnings to those wishing to deploy thru-tubing gravel packing technology in existing wells.
The field in which took place the remedial intervention discussed in this article is located offshore West-Africa, in the gulf of Guinea. Oil is produced from unconsolidated sandstone formations of Miocene/Pliocene reservoirs. Currently, out of 360 wells drilled in the field, about 140 wells are still in production and nearly all of them are equipped with sand-control. Historically, the wells were completed as vertical or slightly deviated Internal Gravel-Packs (IGP), Open-Hole Gravel Pack (OHGP) with milled-windows or with Pre-Pack screens, then since 2001 as Frac-Pack and High Rate Water-Pack (HRWP).With the first development dating back from 1978 (over 30 years of production) and 50% of the producing wells older than 20 years, this asset is clearly a mature field. Therefore, the durability of sand control systems has been dearly challenged and on some wells, failure of the sand-control has occurred before the production had been exhausted. This paper will present several rig-less operations that have been performed for sand-control remediation in this mature offshore field environment and the results obtained.We will first discuss possible scenarios of failure of the existing sand-control completions and then present the choices that have been made for the sand-control remediation, in particular the use of premium through-tubing sand screens with no gravel placement and the use of swell packers for the screen anchoring rather than mechanical devices.We will then present the productivity and longevity achieved with such equipment and will demonstrate that even in some unorthodox cases, as can be often found in mature fields, remedial sand-control operations can still prove successful. Practical aspects that are important when considering such operations will also be covered.Finally, recommendations and lessons-learnt derived from successes and failures will be presented. Description of the SituationThe reservoirs produced are buried between 1200 and 1500m in TVD (water depth ranges from 5 to 35m). The sandstone formations are unconsolidated to poorly consolidated (slowness are in general > 120 µs/ft). Permeabilities vary from a few hundred milidarcies to ~2 Darcies. The sands encountered are fine to very fine with D 50 between 100µm and 250µm. X-ray diffractions indicate a very high clay fraction which is often found above 25-30% and that is confirmed by solubilities in Mud-Acid (HCl-HF) of the same range (Table 1). The majority of the clays are of migratory type (mainly Kaolinite, some Illite) and the formations often exhibit high sensitivity to fresh water. During coreflood water sensitivity tests, fines mobilization is hence frequently observed; sometimes to a point where the term "fluidization of the formation" was mentioned in laboratory reports.In view of the formation characteristics, all producers have had to be equipped with sand-control equipment regardless of which reservoir has been completed. As the Frac-Pack and HRWP techniques were introduced only around 2001, i.e. 20 years after the first develo...
Sand production is naturally occurred in Miocene-Pliocene clastic reservoirs. To develop the well throughout the years of field experiences, sand production management during the very early and late stages of well life, as a result of depletion of reservoir pressure has brought up many challenges, especially in terms of field potential sustaining, well productivity and investment justification. Thru-tubing gravel pack (TTGP) is one of the options considered for sand control remedy. Placing gravel into the annulus of tubing-screen and tubing- blank section which similar principle as circulation gravel pack and can be deployed in various methods using wireline, coiled tubing, or bull heading without the need for workover or rig operations. Based on field experience, the coiled tubing considers more efficient method for thru tubing gravel pack compared to wireline conveyance, i.e., using a dump bailer. But the drawback of conventional thru tubing gravel pack (TTGP) is the high skin value because the gravel only fill up in the annular section as above mentioning. Perforation damage still generate additional skin, smaller ID of the screen, finally end up with shorter well life expected. The most effective placement techniques are by squeezing the gravel to pack in the perforation and possible void space in the reservoir with the coiled tubing. It has been proven method for minimizing the production of sand-fines, reducing perforation damage, and prolonging well life. But the successful squeezing the gravel to pack in the perforation and possible void space in the reservoir via coiled tubing the challenge operation, especially on 3-1/2" Monobore completion with 1.5" OD of coiled tubing. The improvement of the through-tubing gravel pack pumping technique, which focuses on improving gravel placement, addresses a problem that needs a solution with utilizing the existing equipment and services. To overcome this limitation, a concept of combining the gravel placement in both coiled tubing and annulus has been innovated, studied and evaluated to eliminate the problem of limited gravel placement. This improvement of thru tubing gravel pack placement technique has been applied field where sand production is expected from both virgin formations and existing depleted zones. The gas potential gain from all implemented wells (11 wells) has observed at 62 MMSCFD at Maximum Allowable Sand Rate (MASR).
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