Unlocking Heavy Oil Potential From Shallow Reservoirs: Successful Cold Flow Testing of Heavy Oil Exploration Wells with PCP Artificial Lift System

Abstract

Abstract The objective of this paper is to describe cold flow well test challenges of heavy oil reservoirs and the successful techniques applied to produce heavy oil from shallow reservoir (500–1000 ft) to surface. Exploration in the State of Kuwait focuses on finding heavy oil from shallow reservoirs. As a pilot heavy oil project of a new field, six exploratory/delineation wells were drilled upto a depth of 1500 ft and completed with 7” casing. A testing process was developed to test and establish cold flow potential of these wells with drilling rig. Testing of each zone was required to collect a primary source of information on production rates, sampling, reservoir characterization and assess reserves for further field development. Progressive Cavity Pump (PCP) was selected as artificial lift method for testing of heavy oil exploratory wells considering low API gravity, high viscosity, low GOR and possible production of sand along with the oil. Real time bottomhole pressure and temperature data were monitored at surface using sensors of the downhole pump assembly. Specialized surface and subsurface equipment were selected to handle sour fluid, liquid rate measurements and to mitigate sand production problems. MDT data acquired during drilling indicates presence of low energy (250-400 psi reservoir pressure), heavy (16-21°API), viscous (100-300 cp) and sour fluid (5-25% H2S) in the targeted reservoir. Cold flow production testing of heavy-oil reservoir presents significant technical challenges such as designing the most appropriate test string, selection of artificial lift technique, safe handling of reservoir fluid with high H2S concentration, efficient handling of produced sand and flowing the well continually. By overcoming these challenges, three heavy oil exploratory wells were successfully tested with PCP test string and suitable surface test equipment to demonstrate producibility of heavy-oil. Multiple zone tests were carried out in each well to estimate the potential of each layers. During testing the wells produced commercial quantity of 16-22° API oil gravity with H2S concentration upto 20%. Extended commingled production test was essential for the design and implementation of a production facility for heavy-oil production. Optimum production rate of each well was estimated by commingling the tested zones & testing individual zones with a wide operating capacity PCP. During testing, sand production was observed initially and at times PCP got stuck with sand. The extended tests of same reservoirs showed very less or no sand production. This phenomenon helped in modifying the production rates during testing. For the first time in Kuwait, a highly sour shallow reservoir was successfully tested and proved the presence of significant amount of heavy oil. This success proves the well testing concept for future applications in the heavy oil fields and paves the way for further development of this new field to achieve company's strategic production targets.