A Case History: Use of a Casing-Conveyed Perforating System to Improve Life of Well Economics in Tight Gas Sands

Abstract

This paper provides the first technical review of a casing-conveyed perforating technique to fracture stimulate multiple sands in a single wellbore. This is an alternate well completion methodology to improve life-of-well economics. Two wells in Kenai, Alaska were recently completed using this system. The system consists of perforating guns mounted external to the casing and integral valves in the casing for zonal isolation. All equipment is remotely actuated without wellbore intervention. The first well was completed with 15 perforating modules and the second with 12 modules, each placed over a 1,700' (520M) gross interval. This case history recounts the installation of these completions and their subsequent perforation and fracture stimulation. Both completions are considered technical and economic successes. The casing-conveyed perforating technique was chosen for these Beluga Sand wells in an effort to improve life-of-well economics and total hydrocarbon recovery. An exhaustive characterization study of this multiple-pay environment recognized that conventional completion techniques were not adequately developing the resource. Low-quality Beluga sand bodies represent a large potential target of reserves, but the economics of conventional completion techniques never allowed this potential resource to be stimulated and properly evaluated. Use of this new completion technique meant that all pay sands, even those low-quality sands that had conventionally been ignored, could now be effectively and economically stimulated. Minifrac data, tracers, and production logs are used to evaluate the productive potential of these low-quality Beluga Sands. Introduction From 1995 to 1998, geoscientists, petrologists, and reservoir engineers undertook an exhaustive reservoir characterization study of the Beluga formation in the Kenai Gas Field. The middle and lower Beluga sands in the Kenai Gas Field are a normally-pressured 1,700' (520M) section characterized by stacked pay with highly variable pay quality. These fluvial sandstones are 5 to 30 foot (1.5M – 9M) thick. Permeability ranges from 0.01 to 3 millidarcies. Mineralogy is complex, including a high percentage of clays, volcanics, coals, and fines as described in Table 1. The framework grains for the Beluga sandstones are metamorphic rock fragments. The sandstones are bounded by discontinuous shale, siltstone, and coal beds. Formation gas is very lean (specific gravity = 0.56) with no condensate, and formation waters contain approximately 5,000 mg/l total dissolved solids. Recovery from the middle and lower Beluga formation in the Kenai Gas Field through 2001 is 51.6 BCF with estimated 260 BCF OGIP. During this reservoir characterization study, it became apparent that conventional completion techniques were not optimally developing the Beluga Sand resource. One problem with a conventional approach is "cherry picking" the best sands in a well for stimulation, which leaves a large percentage of pay unstimulated. Unstimulated sands contribute little to a well's productivity. Attempts to stimulate a higher percentage of pay dramatically increase the development cost, especially in an operating environment with limited services and infrastructure. Worse perhaps was that conventional completion techniques prohibited evaluation of low-quality Beluga sands to determine whether they could be commercially developed and added to the reserve base. These low-quality sands in the Kenai Gas Field were identified as a potential 70 BCF recoverable target if they could be commercially developed.

Post Frac Evaluation of Multiple Zone Fracture Treatments Using the "Completion Efficiency" Concept

“…Major advances have been made in recent years in both coiled tubing fracturing and in casing-conveyed perforating (the "Excape" system). 19 These advances have the potential to reduce the cost of multiple stage treatments by allowing for multiple frac stages to be treated in a single day.…”

Review of Current Fracture Stimulation Techniques for Best Economics in Multilayer, Lower-Permeability Reservoirs

“…Eller et al 14 gives us the first technical review of a new casing-conveyed perforating system (CCPS). This paper reviews the application of the process to two wells in the Kenai Gas Field in Alaska where it was used to fracture stimulate multiple sand bodies in the Beluga formation where "…the economics of conventional completion techniques never allowed this potential resource to be stimulated and properly evaluated."…”

“…The first of these is a process where perforation guns are deployed with (attached to the outside of) the well casing before cementing, and selectively fired. [14][15][16] Added to this unique perforating approach, remotely actuated flapper valves within the casing jewelry serve as the isolation mechanism between zones. 2.…”