Perforating Monobore Completions Offshore: An Efficient, Safe and Optimal Approach

Abstract

Monobore completions have been installed in wells as far back as the 1980's. Early examples were reported in several SPE papers by companies such as Santos, Total and Unocal (now Chevron). The main drive being reduced drilling and completion costs. Perforating monobore completions is also not new and there are several methods to deploy guns into these types of well completions under various conditions (underbalance, overbalance or dynamic underbalance). Reservoir performance can be optimized through perforation modeling where analysis has shown that a tailored Dynamic Underbalance (DUB) approach can deliver productivity gains from 5% (shallow mud filtrate damage) to 40% (deeper mud filtrate damage) higher than traditional perforation techniques. This is a data driven optimization based on field data such as zonal permeability, pressure, temperature, fluid shrinkage factor, fluid viscosity, GOR, wellbore trajectory and completion design. To achieve maximum gain, multiple perforating runs on wireline are required; however this approach is often discounted (with well life production sacrificed) in order to achieve rig efficiency targets within the constrained economics of monobore completions, and to limit HSE exposure. This paper discusses a pragmatic approach to perforation optimization focusing on the specific alignment of economic, technical and safety related aspects within oilfield operations. The context of this approach applies to the techniques used to avoid rig critical path altogether, thus removing rig cost from the equation and refining the approach through a data driven workflow utilizing acquired DUB pressure data. This approach describes the combination of the key components in detail, including latest shaped charge design and perforating technology, workflow optimization, operational risk and execution approach. Results within this case have led to a standardized workflow within monobore completion delivering more than 24 days in operational savings over a 12 month period, and post perforation nodal analysis showing gains of up to 40% within a mature asset.