RIASSUNTO
Abstract
In many oilfields the relatively small number of high-cost, highly productive wells, coupled with a carbonate and or 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 new fields such as frac packs for sand control and acid stimulation for carbonate reservoirs has 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 where applied.
This paper presents 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 carbonate reservoirs. The combined treatment has the potential to provide cost savings with a single mobilization for the combined treatment. The paper will describe the laboratory testing that was performed to qualify the treatments for two carbonate reservoirs (black oil and HT gas/condensate). In the test program assessment was made of oil, brine and gas permeability prior to and following application of the stimulation packages. The chemical packages assessed included classic HCl formulation and chelant stimulation chemicals on their own and with inclusion of scale inhibitor chemicals to provide simultaneous stimulation/squeeze treatments. These formation damage results and chemical return profiles were then compared to coreflood test results with scale inhibitor applied as a typical squeeze treatment. Results for these studies show that under matrix flow conditions inclusion of even highly compatible scale inhibitor resulted in formation damage due to chemical/rock/brine incompatibility during the stimulation process. Details of the solution to this problem are outlined within this document.
Introduction
The combining of scale squeeze treatments with matrix stimulations has the potential to bring cost savings to wells that have a need for stimulation due to either generation of primary production or removal of completion/production related damage and have a positive scale tendency that cannot be effectively treated by downhole chemical injection if installed. The following section outlines the mechanism of scale formation and formation damage these treatments are designed to control and remove.