Karachaganak is a gas condensate field in western Kazakhstan's pre-Caspian basin. The reservoir is a heterogeneous carbonate rock. Oil-based fluids are not extensively employed in stimulation due to their costs. The paper's objective is to describe the issues the operator faced and that led to the field trial of an oil-based stimulation fluid, fluid selection process and the results of the successful application of this technology as a cost-effective means of improving Karachaganak stimulation operations.
KPO finds horizontal wells completed with multi-stage stimulation sleeves isolated with swell packers installed in 6″ open hole as most suitable and efficient method of construction of oil production wells in the Karachaganak field. However, stimulation of wells such as these creates the potential for injection of large volumes of water into the formation which can result in lengthy well cleanups. To provide a solution to this problem KPO instigated a field trial of an oil-based fluid in stimulation.
Water-based linear gel, used as a displacement fluid, comprises the largest part of pumped water volumes. Therefore, replacing gel with an oil-based system would lead to a drastic reduction in the amount of water injected. In the course of a close collaboration with the Service Company, an oil-based stimulation displacement fluid was selected basing on laboratory testing that considered the effect on both the formation and the surface production facilities. A successful field trial then followed that showed reduced clean-up time (and, consequently, reduced greenhouse gas emissions), potential cost savings, and accelerated production. KPO then continued with the use of the oil-base fluid system, and the results of the trial were replicated. The success of the operations shows there is potential to further optimize the nature of stimulation fluids with the intent to decrease injection volumes. In addition, a market investigation of alternative base fluids is currently in progress with the aim of further reducing cost while still continuing to get the benefits resulting from the use of oil-based stimulation fluids.