Solids Handling for Upstream Oil & Gas Industry: Putting All Five-Steps Together (OTC-24705) (B-FSM040)
Paper OTC-24705-MS provides and excellent case study of applying the Five-Steps of Sand Management. This is the largest offshore Facilities Sand Management system in the world, and I had the privilege with working with an outstanding company (Murphy Sabah Oil Co.) and world-class people in design, build, install, and commissioning. Please read the paper for full details.
Introduction
A deepwater field located offshore Sabah, East Malaysia, with an average water depth of approximately 1300 m, features a spar dry tree unit and multiple subsea hub tie-backs to an FPSO. In early 2011, several of the wells on the spar began producing solid fines that affected production. To sustain and maximize production, the operator initiated three separate measures to control the solids. It was decided that a long-term solution would be to re-complete the affected wells with enhanced downhole sand control on the lower completions, such as open-hole gravel pack and cased-hole frac packs.
The short-term solution consisted of installing a topsides Sand Management System on the spar to remove solids at the wellhead prior to the choke and sand sparging equipment on the FPSO separators to remove buildup of sand that was produced by the subsea wells and any solids that bypassed the spar. This paper focuses on the spar topsides sand management system that is unique in its size and scope.
It includes ten wellhead desanders, a common slurry transportation system, a dewatering and bagging station, and a skip removal system to process up to 10 tons per day of solids. Current work is underway to upgrade the system to include an integrated sand cleaning package that will allow the overboard discharge of the solids, which will be a first for Malaysian waters.
The sand management system and the first wellhead desander were commissioned in October 2011, and by April 2012, a total of six wellhead desanders were on-line. Upgrading the spar with topsides sand management system has effectively controlled the production of solids and maximized hydrocarbon production during the same period.
Step 1: Separation
Ten wellhead desanders were installed on the dry-tree wellheads upstream of the choke. Each unit is designed at ASME 1500# rating and contains a 10” cyclonic insert. The desander has a separation size of 16 microns and the sand is collected into secondary 600-liter accumulators.
Step 2: Collection
In addition to using the 600-liter accumulators (one per wellhead desander), the collection system employs a piping header to transport the collected solids to a central gathering station. This header uses utility water to transport the depressurized slurry.
Step 3: Cleaning
A cleaning station was retrofit to allow recirculation/attrition batch scrubbing of the removed sand. This station is designed to treat 32 tons/day of sand to <1 wt.% oil on dry sand. The incoming (dirty) sand had only 0.25 wt.% oil on dry sand, and this station was used to ensure compliance with environmental discharge requirements.
Step 4: Dewatering
A two-stage central dewatering station was used to remove all free-water from the slurry discharged from the ten accumulators. Slurry from the piping header is directed first to a bank of desilter cyclones which remove 90% of the liquid, followed by an open dewatering bag four-place system for final water removal. Water from the first stage goes to closed drain and water from the second stage goes to open drain.
Step 5: Transport
There are two transport-to-disposal routes. Initially the dewatered sand was transported via crane lift to a skip, then the solids brought onshore to a landfill. After the cleaning station was installed the slurry is transported by pipe to overboard discharge.
The next article summarizes the discussion on the Five-Steps of Sand Management with a decision tree, key items, and technical paper references.
References
- Loong, Y., Rawlins, H., and Goo, D. 2014. Upgrade of Spar Topsides with Comprehensive Facilities Sand Management System. Paper 24705-MS presented at the Offshore Technology Conference-Asia, 25-28 March, Kuala Lumpur, Malaysia. https://doi.org/10.4043/24705-MS
