Heavy oil reservoirs have became a key and difficult point as exploration and development of oil and gas goes deeper. Since deepwater heavy oil reservoirs are characterized by adverse fluid property and poor flowability resulting from low seawater temperature, conventional well test usually fails to gain expected crude sample and real formation data, leading to some problems for subsequent development. In view of two difficult issues during the deepwater heavy oil reservoirs test – flow assurance concern and decision-making difficulty in testing system, application of appropriate test technologies and techniques are of great importance.
Prior to the offshore test, an integrated approach to modeling and designing operating conditions was described. The feasibility of available technical solutions in relation to enhancing the low wellhead temperature conditions was discussed based on the wellbore temperature and pressure features derived from the analytical modeling, and a test technique (integrated progressing cavity pump (PCP), heating sucker rod and insulated tubing) applicable to deepwater heavy oil reservoir was recommended. Then, drilling-stem test (DST) was carried out to an exploration well with two oil layers and one gas layer which is located in southwest of Congo sea with the recommended test technique.
Simulation results demonstrate that the advantages of the compound technology – electric heating, PCP and insulated tubing are far greater than using insulated tubing or heating sucker rod alone. Compound technology decreases the frictional pressure loss of the producing fluid due to its capability of maintaining high and uniform wellbore temperature. Interactive tubing conveyed perforating (TCP) and DST was conducted with a testing program of thrice flow well and twice shut-in well. Insulated tubing assembly was employed from progressing cavity pump stator to the wellbore and the setting depth of the heated sucker rod was down to about 10m above the pump. Productivity information, representative crude samples and pressure/temperature information of the testing zone were obtained successfully.
The simulation technology and pilot test proved the feasibility of insulated tubing and electric heating PCP in deepwater heavy oil testing, providing technical guidance for further appraisal and development of deepwater heavy oil fields.