This paper describes the conceptual and early development phases of a completely new approach to flow profile logging in extended reach horizontal water injectors.
Extended reach drilling technology (ERD) has enabled the economic development of many fields containing hydrocarbons in low permeability formations or reservoirs with thin columns. This is particularly true for offshore fields where development from a reduced number of surface locations carries significant cost benefits, or where fields are developed from onshore locations and ERD wells are drilled to develop resources offshore(2, 5). Maersk Oil has a proud tradition of being at the forefront of ERD drilling and has set a significant number of world records in this area since the mid 1980's – both in the Danish offshore sector and more recently offshore Qatar. Figure 1 shows the current ERD drilling envelope. As fields become more mature, there is an increasing requirement for flow profile logging and interventions to correct unwanted flow profile anomalies such as water production from fissures, gas cusping, etc. Particularly in waterflooded fields developed with ERD wells, logging of flow profiles in extended reach water injection wells is an important method used to ensure that the lateral sweep of hydrocarbons into production wells is maximised and ‘short circuits’ are idenified and remediated.
Well trajectories have become increasingly more challenging for re-entry to conduct such flow profile logging operations using conventional technology. Aspect ratios (the ratio of TVD verus departure) in excess of 1:10 are not unusual. A typical well drilled in Denmark has a horizontal section of 20,000 ft length at a true vertical depth of some 8,000 ft. In Qatar typical wells have a 20,000 ft long reservoir section at a true vertical depth of 3,500 ft. Coiled tubing conveyed logging operations are limited in reach due to friction and consequential buckling of the tubing. Tractor operations are hampered by scale or debris and also suffer from limitations due to the available cable strength when the logging assembly needs to be retrieved following a potential tractor power failure deep in the well. The common use of barefoot completions in such wells further complicates matters since formations may be mechanically weak and wellbores may exhibit washouts, making tractors currently on the market less likely to succeed in conveying logging tools to the required depth.
In view of the challenges listed in the preceding paragraph, a concept for an un-tethered, autonomous logging tool was developed late 2008. A series of patent applications were filed during 2009 and 2010 in support of the concepts described here. This paper describes the concept and expands on the different stages of the development of this tool, through conceptual design and into flowloop testing. At the time of presenting this paper, the final field testing phases are being conducted in preparation for the first application in an ERD injection well. The paper presents the results of the initial flowloop and field tests to demonstrate that this logging method is a viable method to log flow profiles in ERD wells and also in regular horizontal water injection wells, when compared with conventional logging methods.
