Chasing Behind Casing Opportunities in a Low Salinity Laminated Brown Reservoirs
Authors: Ramly N. F. Noor Faezah Ramly , Ashqar A. Ayham Ashqar , Bakeri F. A. Fahmi Amni Mustafaal Bakeri , Dahlan N. A. Nur Athirah M Dahlan , Ling R. P. Ling Ru Piin , James S. M. Sylvia Mavis James , Yusuf M. H. M Hafizi M Yusuf , Jamaluddin J. Junirda Jamaluddin , Karim M. A. M Azan A Karim 
Published: January 2020

Considering the oil prices hovering at low levels, opportunities to reduce the cost and enhance productivities becomes the new routine, to improve the net present value, and reduce operating cost. Field A is located offshore West Malaysia with production started in 1960's. Idle or uneconomic producing wells went through detailed study to identify and appraise possible behind casing opportunities prior to plug and abandon. The detailed assessment targeted to verify hydrocarbon-bearing sands, in reservoirs known to be fine to very fine and interbedded silts and clays layers.

To identify the present behind casing hydrocarbon saturation, and assess reservoir depletion, advanced pulsed neutron capture surveillance is used in the low contrast reservoir. A combination of elastic and inelastic pulse neutron logging, supplemented with total organic carbon (TOC) was carried out. TOC, Sigma, and near to far detectors were used to ascertain the presence of hydrocarbon. Results were compared to the open-hole saturation to identify possible depletion, and differentiate it from annulus-trapped hydrocarbon. Completion was cemented and considered as a new casing. Two self-oriented perforation runs were carried out in each interval to ensure penetrating the two casings into the reservoir.

Results coming from pulsed neutron capture indicated presence of HC in various reservoirs; these results were cross-confirmed by sigma and carbon/oxygen logging. TOC computed oil volume is compared to the CO yields computed oil volume, and Sigma derived saturation to identify water bearing zones. Fluid typing was carried out to confirm the fluid properties are not changed. Contradicting results were looked into and verified. Sigma derived saturation was found to be influenced by complex lithology patterns such as carbonate and coal streaks. False HC indications such as behind annulus trapped oil and gas were identified using combination of thermal and burst rations with far and deep late capture curves. Redistributed saturation lead to firming new opportunities that were not considered earlier. Identified prospects were later categorized, and further allocated between long and short strings to minimize depletion and maximize well potential. Tubing annulus is cemented to ensure zonal isolation and ensure well integrity, as a result, two runs of perforations were planned for each interval to increase depth of penetration and improve productivity. The use of all available data allowed to derisk planned perforations and add additional resources.

The developed workflow enlightens the best practice to budgetary recomplete low producing offshore wells. The niche low cost data acquisition, and assessment maximized and ascertained reservoir potential and ensure all available opportunities are looked into without being misled by late well life completion, cementation problems accumulated over time. The followed workflow ensured booking the additional reserves and allowed bringing well back to life at low cost.