Abstract

Exploration activity on heavy oil is steadily gaining momentum in the state of Kuwait. Recently, discovered heavy oil in deeper low permeable Lower Cretaceous reservoir from exploratory wells drilled in two different fields of West Kuwait area at around 11,000 ft. depth. Drill stem testing method was applied to test these exploratory wells. During testing, there was inflow of heavy oil of API 21-22 deg, but the well could not be produced naturally in spite of repeated attempts. Matrix acid stimulation treatment was done to improve the productivity of the reservoir. Well-flowed heavy oil and then gradually ceased to flow. Due to viscous nature, low mobility and low reservoir energy, self-flow could not be sustained. These pose significant challenges for well cleanup, flow studies and collection of representative sample for PVT analysis and fluid characterization.

As no other lifting methods were available, Coiled Tubing was lowered and the well was lifted continuously with nitrogen for cleanup and to assess production behavior. Surface Sampling was not favorable due to mixing with lifting nitrogen gases and only alternative method available was to collect Bottom-Hole Samples (BHS). However, proper cleanup was an issue for sampling operation. Therefore, compositional analysis was done on the lifted sample to quantify the contamination level in the produced fluid before lowering the down-hole sampler in order to capture representative samples. As a result of this approach, representative samples could be captured and fluid characterization could be carried out with quality results which will add value to future reservoir study and modelling. Based on the successful results, it has been planned to use similar approach for sampling in such conditions.

Methodology adopted to overcome challenges faced for sampling and characterization of heavy oil in deep as well as in low permeability reservoirs will be presented in this paper.

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