Offshore Low-Moderate Perm Oil Plays Need Rigless Multifracture Stimulation Completion Plan

Abstract

Abstract After hydrocarbon prices suffered freefall in late 2008, many North America operators responded by increasing the percentage of horizontal completions in low-permeability oil and gas reservoirs to maximize their return on investment (ROI). The US market soon had more horizontal rigs running than vertical rigs. By the end of 2010, the horizontal-to-vertical rig ratio was ~1.8:1, thus leading to the strengthening of another market trend: low gas prices causing many operators to move as much new investment to oil plays as possible. Very few seem concerned about the future of oil prices except that a controlled rise was needed to avoid excess economic pressure on somewhat fragile economies that depend on oil. Higher prices and many maturing conventional oil fields can only encourage offshore operators to pursue their more marginal oil reserves. However, instead of following the historic offshore methods and models for well completions, operators need to closely examine what has transpired in North America during the past 5 to 7 years. There, drastic changes to completion models were required to profitably pursue low- to very low-permeability reservoirs; first in the gas markets and more recently low-permeability oil reservoirs. The primary focus of the "North America Shale Model" is two-pronged: the first part is to use long horizontal sections, but the second part to consistent economic success has been completions that enhance the ability to achieve both adequate fracturing injection rates and effective isolation of hydraulic fracturing stimulation stages. Simply stated, the horizontal completion must be very "frac friendly" to be economic. This completion model is already beginning initial evaluation for shale (source rock) gas reservoirs on several other continents. However, most recently, this same basic approach has been seen migrating to low/ultralow oil reservoirs in North America. However, much larger promise of reward globally will be offshore. For low-permeability offshore fields, a necessary goal will be to drain significantly more reservoir per well than historic completion methods allowed by using long lateral lengths that are concentrated in only the better part of the reservoir. The more traditional offshore "horizontal" model has been to get 1.4 to 1.5 times more exposure to each reservoir layer (60 to 70o laterals) and to complete in multiple layers to "get oil from all the zones" without significant stimulation applications. A more profitable completion model is to also mimic the most recent North America oil/gas-liquids model: maximize drainage from the zone with the highest production potential—single-zone, long horizontal completions with effective multistage hydraulic fracturing stimulation. Most people comprising the oil and gas industry have come to expect that great oil and gas fields are "discovered." What is now being witnessed is major gas and oil fields that are being "unlocked" through innovation. It is proposed that what has happened during the past decade in the US might only be the tip of the iceberg once operators worldwide start to accept this new completion concept on a global basis.