Open-hole gravel packing in vertical/conventional wells is an accepted sand exclusion method that has not gained wide and rapid application in horizontal wells. The reason is largely due to sand placement challenges in the horizontal drain that could lead to premature sand screen-out. Consequently, many operators are skeptical gravel packing horizontal wells since failure could probably result in enormous capital risk. In the Niger Delta, about 70 % of the hydrocarbon-bearing reserves lie in shallow unconsolidated reservoirs where the sonic transit time vary between 110 to 140 us/ft. Production from these intervals has proven record of sand threats to operating cost, well integrity, surface facilities and production sustenance. The challenge is to complete wells in these reservoirs with sand exclusion materials that would guarantee full life-cycle production performance.
Early horizontal wells in the region were completed with stand-alone screens, but recently, the expandable sand screen (ESS) took a leading edge. Though the ESS has a higher inflow area compared to other screens, its high cost, lack of full-bore expansion and the required lead-time continue to raise concerns especially when considered for applications in brown field development where well potential and reserve rewards are low. In response to these concerns, in 2002, openhole gravel packing (OHGP) in a horizontal well was investigated and considered as an alternative sand exclusion option in Shell Petroleum Development Company (SPDC). The trial candidate, the Obigbo-North QWSB-3 was selected and successfully completed as the first horizontal OHGP in SPDC using the alpha-beta wave concept.
Based on simulation results, about 9237 lbm of sand was planned for placement in 1000-ft of 6.0-in hole size, however, the actual sand pumped was about 10830 lbm. This represents an estimate of 6.25-in drain hole size. The application saved over $0.3 million when compared to the cost of using ESS. For the Eastern asset team that drills an average of 12 wells annually, an annual projected completion cost-saving of some $3.6 million is achievable.
Based on the initial production testing, Obigbo-North Well QWSB-3 tested 3250 BOPD with a productivity index (PI) of 130 bbl/(psi-D). Baseline Memory Production Logging Tool (MPLT) logging showed that the entire drain section completed on the clean sand member had effective inflow into the linerbore. In addition to establishing confidence in the application and performance efficacy of OHGP, this trial and the significant cost-savings will engender a paradigm shift to horizontal well sand control. In this presentation, we will share some data and results based on field experiences, challenges and new understanding.
Introduction
This paper discusses the first application of horizontal open hole gravel packing as a sand control method in SPDC. The paper further demonstrates the evaluation of the inflow profile (based on memory production log) as a yardstick for determining the completion efficiency, and reveals the economic argument against using ESS as seen in Well QWSB-3 (figure-1) located in the Obigbo-North field of Niger Delta, Nigeria (figure-2).
Production "hot-spot-effects" a phenomenon characterized by massive inflow into the liner-bore at a particular point (figures-3โ5) is a common phenomenon in horizontal wells completed with stand-alone screens and ESS (that are not fully expanded to the sand-face). The problem is attributed to differential plugging of the completion screen by the migrating formation fines and/or improper horizontal drain section clean out2,3,4. When a stand-alone screen is partially plugged, the resultant annular flow converges to a point where intense inflow into the liner-bore is observed. This problem leads to higher drawdown, liner erosion, sand failure and ultimately production decline1,10. These problems commonly associated with wells completed with stand-alone screens, led to the many recent applications of ESS by the SPDC Land Asset Team. However, high material installation cost and complete expansion remain key challenges in ESS applications. SPDC decided to try horizontal OHGP as an alternative sand exclusion option that will be cost-effective and capable of sustaining production. Consequently, a trial application was executed at the end of the second quarter of 2002 in Obigbo-North Well QWSB-3. The well was planned to develop some 8.5 Million STB from the D3.200A reservoir at an initial offtake rate of 3000 BOPD (tables-1,2).
