Dietmar Neidhardt
Oiltools International (Cayman) Ltd.
Dubai U.A.E.
The use of corrugated pyramid screens on a dryer in second stage mud and cuttings cleaning helped recover a large volume of oil-based drilling mud to save more than $60,000 in mud costs.
Amoco Sharjah Oil Co. has conducted an extensive drilling program in the Sheikdom of Sharjah since early 1994. In a 67-day period of drilling, the company recovered 1,255 bbl of mud, saving $62,750 in mud costs. The net savings for the period totaled $35,815, about $535/day. No dollar values were placed on environmental benefits.
A key to these savings was a High G Dryer from Derrick Equipment Co., equipped with corrugated pyramid screens. Oiltools International Ltd. supplied the solids-control services for Nabors Rig No. 128, including three Derrick Flo-Line 48 Plus Cleaners, one Derrick High G Dryer, and two S2-1 fully hydraulic centrifuges, all serviced by an engineer (Figs. 1 (79477 bytes) and 2). The centrifuges can operate either in solids removal or in barite recovery.
Because of previous experience and thorough knowledge of geological sequences, Amoco Sharjah typically completes a 12,000 It well in the area in about 4 weeks. The wells are usually drilled with oil-based mud, as was the 16-in. hole section on this well.
DRYER
Routine analysis of equipment parameters, such as throughput rates and separation factors, showed that a substantial amount of mud was discharged with cuttings into the waste pit. To try to eliminate this mud loss, Amoco Sharjah put into service the recently developed High G Dryer, The dryer has an elongated screen bed and high-G linear-motion separation which are suited to recover residual oil on cuttings at a second separation stage between cuttings discharge and entry into the waste pit.
Amoco Sharjah approved a 3-week trial of the High G Dryer. The unit characteristics include 0.19-in. stroke with two 1,775-rpm motors (60 hz power) producing an 8G acceleration force. It can be fitted with four 48-in. x 30-in. screen panels.
Special skids were built and explosion-proof augers were installed under the shaker discharge assembly to adapt the dryer to the rig. This work was completed during a 4-day rig move, so the dryer was available at spudding.
TEST WELL
The test objectives included the following:
- Recover cuttings from shale shakers to dry them and optimize free mud recovery
- Use finer mesh screens than normal because excessive mud discharge could be recovered over the High G Dryer
- Create a "last line of defense" to prevent any mud from spilling over the shaker caused by screen blinding
- Reduce any environmental impact from oil discharged into the pit, thus reducing the amount of oil ultimately to be treated or removed
- Evaluate the value of recovered mud vs. rental and screen costs for the dryer
- Determine if tripping could be reduced through improved hole conditioning and mud make up because of second-stage cuttings cleaning for difficult formation intervals.
The results from the 3-week test were encouraging; Amoco then kept this new equipment as a permanent part of its solids control for the remaining drilling program.
Since the initial test, additional wells have been drilled with this cleaning system. Table I (14917 bytes) lists the economic benefits of this cleaning system.
The auger capacity was initially considered a bottleneck, but the augers proved capable of conveying solids at drilling speeds of 200 ft/hr in the 16-in. hole section with peak drilling rates of 500 ft/hr, which produced 124 bbl/hr cuttings volume.
In some hole sections, specific formations caused screen blinding, and a large mud volume (up to 200 b/d) discharged over the shaker. These volumes were successfully recovered by the High G Dryer.
Furthermore, the new pyramid screens reduced screen costs to half that indicated in initial testing.
PYRAMID SCREENS
The corrugated surface on new pyramid screens provides a surface area exposed to cuttings that is 40% greater than that on a conventional flat-surface screen. The increased area improves throughput up to 60%. The upper section of the corrugated screens provides continuous self-cleaning action while the liquid pool accounts primarily for the improved performance.
Data on screen life show the pyramid screens outlast flat screens by a factor of three to four. The manufacturer claims additional benefits, including a deeper pool depth and improved fluid profile with screen peaks exposing more open area in the pool as solids channel in the valleys. Thus, finer mesh screens can be used.
Screen costs during subsequent deviated section drilling (5,200-12,935 ft) dropped to $2,630 compared to $5,925 for the previously drilled section of 5,200-13,020 ft. The screen consumption cost dropped to $0.34/ft instead of $0.75/ft, a 55% improvement.
The use of the high-G type dryer provided excellent results.
During hole intervals characterized by fast penetration rates and sticky clays, solids control should be maintained continuously. Additional mud saved will usually more than justify any additional service charge.
ACKNOWLEDGMENT
The author would like to thank drilling foreman Bobby Rowe and the personnel of Amoco Sharjah Oil Co. for their assistance in helping design the system described here and for Amoco Sharjah's permission to publish the article.
Copyright 1995 Oil & Gas Journal. All Rights Reserved.
