No abstract

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.

As the operator, CNOOC completed drilling two exploratory wells in a deep-water field of the Republic of Congo from May to November of 2013, in 600 m of water depth. Indications of oil and gas- heavy oil layer, gas layer and thin oil layer were found in the E-1 well according to logging data analysis. There are many challenges for the operator and service companies to perform the appraisal of this heavy oil reserve in a deep-water offshore environment, such as operational cost control, low temperature near the seafloor/mud line, heavy oil flow assurance, sand control, etc. In order for the well test to be effective, all the above issues must be fully understood and methodology employed that will reduce the chance that operational risks will occur. This paper presents an integrated well test program of the E-1 well developed and implemented for reservoir characterization and formation evaluation in the Congo basin. The program used a combination of various formation evaluation techniques such as wire wrapped screen sand control, PCP with electric heating rod and insulation tubing, hydrate prevention, emergency response in complex condition. The integrated well test program was designed and modified to meet the project delivery timeline and cost constraints, while responding to the challenge of properly testing the oil/gas reservoirs. This paper also gives the data analysis results and summarizes the encountered problems and learned lessons from field operations. The treatment practices and gained experiences from the field operation presented here provide valuable guidance for future deep-water heavy oil exploration and development operations.