Mini Fracturing: A New Horizon of Breakthrough Integrated Technology for Small Fields.

Abstract

This paper presents a case history of a slickline propellant stimulation treatment performed in a well at the Penara and North Lukut field, which is a small oil field operated by PETRONAS Carigali offshore Peninsular Malaysia. The stimulation was performed using propellant that rapidly burns to create a high pressure gas pulse, which in turn breaks through damage in the perforation tunnels and near wellbore, effectively creating fractures through the damaged zone to enhance well productivity. The Penara and North Lukut reservoir pressure is around 3000psi with a bottom hole temperature of 258oF. The Crude has a medium gravity of 32 API, however it has a low GOR and high wax content with a tendency for heavy wax deposition. Frequent scraper runs are required to prevent excessive wax deposition in the low rate wells which have well head flowing temperatures below the wax cloud point temperature. Nowadays, slickline, due to its light weight, is widely used to perform well interventions and perforating operations on small platforms. Conventional CTU and E-line are often too heavy to be lifted on board by the platform cranes. Since field production start up in August 2004, slickline has been successfully used for well interventions to change out gas lift valves and to carry out regular tubing wax scraper runs. Slickline with 0.108"stainless steel wire was used to convey the propellant stimulation guns. Propellant simulation software was used to simulate the downhole pressure response to ensure that well integrity would not be compromised and to help select the optimum gun size. For each treatment one 10 foot, 2 inch OD gun was used. An additional unique feature of the tool string was the gun firing mechanism which utilized a coded sequence created from variation of surface jerking rate to generate its firing command, providing reliable and safe gun activation. Lastly, this paper also details the results of the propellant stimulation treatment which significantly enhanced the productivity of the treated well. Introduction The Penara and North Lukut field is located in the northeastern fringe of the Malay Basin in South East Asia, approximately 300 km offshore Terengganu, Malaysia in a water depth of 62 m and at the time of development was considered to be a marginal field. The field has been developed using two monopod platforms, one at Penara and one at North Lukud, both of a lightweight structural design (Figure 1) featuring an integrated deck and topsides concept connected via sub-sea pipelines to a Floating Production, Storage and Offloading (FPSO) vessel. The Penara reservoirs are of early miocene age deposited under fluvial environment with meandering stacked channel systems. The sands exhibit a fining upwards sequence of multiple stacked channels sands. The Penara well was initially drilled to target the I-65 oil sands. I-65 was however found to be wet with the well sidetracked twice. The two initial pilot holes were eventually plugged back and the well was completed with 3 ½ inch tubing as a single selective oil producer in 4 zones K-5, K-10, K-20.5 and K-50.1. (Figure 2) Based on open-hole logs obtained from Logging While Drilling operations, K-20.5 is an argillaceous sand with significant amounts of silt and clay content. It has a net to gross of 0.47 and a net pay of 7.3 m with average Sw of 47.18% and average porosity of 12.48%. The K-50.1 is a better quality reservoir with some silt and clay streaks. The net to gross is 0.92 while the total net pay is 20.3 m with average Sw of 56.42% and average porosity of 15.42%. K-20.5 and K-50.1 are separated by a shale break.