Abstract
Curing severe to total lost circulation in naturally fractured/vugular formations has always been challenging, especially across the Middle East. In these environments, conventional particulate lost circulation materials (LCMs) are seldom effective due to the uncertainty on the sizes of the formation openings through which losses occur. This paper presents lab evaluation data, supported by field experience, of using a combination high fluid loss squeeze (HFLS) and reticulated foam LCM (RFLCM) treatment.
The LCM treatment was designed and qualified based on successful laboratory tests sealing slots up to 40,000 microns. Laboratory and field results are presented from the dual HFLS and RFLCM technology application in two countries in the Middle East: Oman and United Arab Emirates (UAE). The details include formation characteristics, hole size, LCM pill volume and concentrations, and the mixing and pumping methodologies used. The success of the applications is demonstrated by presenting the loss rates before and after applying the treatments, in static and dynamic wellbore conditions, and illustrates savings in terms of rig time.
In Oman, the subject wells experienced static losses up to 125 bbls/hr and dynamic losses in the range of 280 bbls/hr (at 550 gpm) to "No returns". The formation was characterized as vugular, and the client's objective was to pump an efficient LCM solution that would cure losses quickly after reaching well Total Depth (TD) and perform logging operations without having to use a cement plug thereby saving rig time. The HFLS and RFLCM treatments were mixed in water, pumped through a circulating sub and a hesitation squeeze was applied. After the squeeze, both static and dynamic loss rates reduced to zero and operations were able to safely continue.
For the UAE applications, the subject wells were drilled with non-aqueous fluid and losses experienced were in the range of 85-200 bbls/hr in static conditions, and 150 bbls/hr to complete losses in dynamic mode (990-1250 gpm). The formation was characterized as naturally fractured. The HFLS and RFLCM components were mixed in base oil, pumped through a circulating sub and a hesitation squeeze method was applied. After the squeeze, static losses reduced to 2-15 bbls/hr and dynamic losses to a maximum of 25 bbls/hr (dropping down to 5 bbls/hr while drilling) allowing operations to recommence.
In technical qualification tests, plugging of a 40,000-micron lab-simulated fracture/vug opening provided confidence that the subject LCM combination would deal with losses to uncertain fracture/vug size downhole. The successful field applications where severe to total losses were cured has validated the HFLS / RFLCM dual approach. The most notable advantage of improved LCM technology is the reduction in well construction costs through decreased rig time associated with curing severe to total lost circulation.
