Numerous opportunities may have gone unevaluated in Norwood Resources Ltd.’s initial two-well program in the remote Sandino basin in nonproducing Nicaragua, a consulting engineer’s report indicated.
In addition to possibly productive formations at the San Bartolo and Las Mesas exploratory wells, the Vancouver, BC, company’s integration of well and seismic data confirmed the existence of 8-10 nearby structures with 2 to 5 sq miles of closure each, using only the productive intervals discovered at San Bartolo as horizons of interest.
Meanwhile, the consulting engineers’ evaluation of logs and drillstem tests from the two wells suggests that several potential reservoirs were damaged during drilling and testing and that large potential may exist in zones thought to be water-bearing or tight (OGJ Online, July 12, 2007).
Zones at 6,764-6,835 ft and 6,210-6,277 ft at San Bartolo are capable of commercial production rates that could approach the initial DST flow rates of 570 and 365 b/d, respectively, with proper cleanup, the evaluation concluded.
Several of the tested intervals, including 8,610-38 ft and 6,380-6,584 ft, were damaged by drilling or completing overbalanced and would require some stimulation to determine their productivity. Acid frac stimulated intervals at 7,014-7,244 ft, 6,135-85 ft, 6,066-6,110 ft, 5,975-6,010 ft, and 5,790-5,885 ft need to be flowed for longer periods to determine their true production rates. DSTs run on damaged intervals caused several zones to be abandoned without testing and considered unproductive, which may not be the case, the evaluation said.
Artificial lift is probably needed, but low-pressure gas in the oil in the successfully tested intervals could facilitate gas-lift production as opposed to installing surface or submersible pumps. This gas probably caused the appearance of gas flows while drilling and the unneeded builds in mud weights that contributed to formation damage.
The interval 3,350-3,460 ft was found to be the most promising at Las Mesas. The interval might produce better than the initial 107 b/d flow rate, but artificial lift is implied.
Intervals at 8,818-38 ft, 8,708-28 ft, 7,846-8,034 ft, and 7,054-90 ft warrant further investigation.
Recoveries at 4,742-4,810 ft and 3,908-4,186 ft are considered invalid because it is suspected that the fluids were from failed squeeze perforations.
The report recommends modifying drilling practices, including single trip tubing-conveyed perforating/DST to maintain underbalanced perforating, sample-chambered DST tools, and possibly air drilling. Avoiding formation damage is of high importance because of the sands’ clay content.
The company is retooling to continue its exploration program at reduced cost and has evaluated rigs in four US states.
