RIASSUNTO
Abstract
In a deepwater West African field the relatively small number of high-cost, highly productive wells, coupled with a high barium sulfate scaling tendency (upon waterflood breakthrough of injected seawater) requires effective scale management along with removal of near-wellbore damage in order to achieve high hydrocarbon recovery.
The nature of the well completion strategy in the field (frac packs for sand control) had resulted in some wells with higher than expected skin values due to drilling fluid losses, residual frac gel, fluid loss agents, and fines mobilization within the frac packs.
The paper will present how the challenges of managing impaired completions and inorganic scale forced innovation in terms of when to apply both stimulation and scale inhibitor packages to deep water wells. This paper will outline a novel process for non-conventional batch chemical applications where bullhead stimulation treatments have been displaced deep into the formation (>20ft) using a scale inhibitor overflush. Not only does this benefit the stimulation by displacing the spent acid and reagents away from the immediate wellbore area, but the combined treatment provides a cost savings with a single mobilization for the combined treatment. The paper will describe the laboratory testing that was performed to qualify the treatments.
The five field treatments that were performed demonstrate how these coupled applications have proven very effective at both well stimulation/skin reduction and scale inhibitor placement prior to and after seawater breakthrough. The term ?squimulation? is used by the local operations team to describe this simultaneous squeeze and stimulation process.
Many similar fields are currently being developed in the Campos basin, Gulf of Mexico, and West Africa, and this paper is a good example of best-practice sharing from another oil basin.
Introduction
The fields are located offshore in Angola in approximately 1,300 feet water depth. The fields are developed with both dry tree wells which are located on the Compliant Tower and subsea wells that are connected to the Compliant Tower via one of three subsea production manifolds. All of the fields are under waterflood. Gas-lift is available for artificial lift. A total of 10 dry tree and 13 subsea production wells have been completed thus far and the development program is still underway.
All but two of the producers are completed with cased hole frac packs. Some wells have multiple, or stacked, frac packs. Two wells are drilled as horizontals and are completed with open hole gravel packs.
The field was started up in January 2006. The Basis of design for managing barium sulphate scale was to scale squeeze the wells at seawater breakthrough. Unfortunately, in the 4th quarter of 2007, some wells incurred seawater breakthrough much earlier than forecast which led to the formation of barium sulphate scale in these wells and significant production impairment1. An ensuing proactive scale management program of both scale squeezes and incorporation of scale inhibitor in the initial completions has resulted in no further scaling events.