Significant emphasis on data quality is placed on real-time drilling data for the optimisation of drilling operations and on logging data for quality lithological and petro-physical description of a field. This is evidenced by huge sums spent on real time MWD/LWD tools, broadband services, wireline logging tools, etc. However, a lot more needs to be done to harness quality data for future work-over and or abandonment operations where data being relied on is data that must have been entered decades ago and costs and time spent are critically linked to already known and certified information. In some cases, data relied on has been migrated across different data management platforms, during which relevant data might have been lost, mis-interpreted or mis-placed. Another common cause of wrong data is improperly documented well intervention operations which have been done in such a short time, that there is no pressure to document the operation properly. This leads to confusion over simple issues such as what depth a plug was set, or what junk was left in hole. The relative lack of emphasis on this type of data quality has led to high costs of work-over and abandonment operations. In some cases, process safety incidents have arisen. This paper looks at some work-over operations carried out in a span of 10 years. Data management system is generally analysed and a categorisation of issues experienced during the work-over operations is outlined. Time lost due to data error was seen to average 1.54% but with a unit peak of 19%. An analysis is done on the wells' activity history to check for correlations. Bottlenecks in data management are defined and solutions currently being implemented to manage these problems are listed as recommended good practices.
Significant emphasis on data quality is placed on real-time drilling data for the optimization of drilling operations and on logging data for quality lithological and petrophysical description of a field. This is evidenced by huge sums spent on real time MWD/LWD tools, broadband services, wireline logging tools, etc. However, a lot more needs to be done to harness quality data for future workover and or abandonment operations where data being relied on is data that must have been entered decades ago and costs and time spent are critically linked to already known and certified information. In some cases, data relied on has been migrated across different data management platforms, during which relevant data might have been lost, mis-interpreted or mis-placed. Another common cause of wrong data is improperly documented well intervention operations which have been done in such a short time, that there is no pressure to document the operation properly. This leads to confusion over simple issues such as what depth a plug was set, or what junk was left in hole. The relative lack of emphasis on this type of data quality has led to high costs of workover and abandonment operations. In some cases, well control incidents and process safety incidents have arisen. This paper looks at over 20 workover operations carried out in a span of 10 years. An analysis is done on the wells’ original timeline of operation. The data management system is generally analyzed and a categorization of issues experienced during the workover operations is outlined. Bottlenecks in data management are defined and solutions currently being implemented to manage these problems are listed as recommended good practices.
Drilling with water based mud (WBM) generally has its green and cost effective advantages but also comes with its own challenges, which raise the need for more vigilance, planning and timely reaction when WBM is to be used for any hole section. On FAQ1X well, the 16″ top hole section was drilled to 9,500fttvd with KCl polymer WBM; while circulating hole clean in preparation for tripping out, erratic mud rheology properties were observed. It took up to 3days to recondition the drilling fluid specifications. An investigation was carried out to explore the possible causes. The behavior bore no similarity to equivalent sections in previously drilled wells, though the mud system was different. The fresh water for building the mud was optimum; the additives were in good condition and within acceptable operating conditions. The analysis for any carbonate contamination by Alkalinity Analysis (which is rather unreliable) gave an indication of possible carbonate contamination though no source of carbonate was detected. The bentonite used was not in excess yet there was an increase in the Cation exchange capacity of the mud. The other source of Low gravity solids is formation solids that have been very well grinded by the bit and dispersed in the mud such that it becomes difficult to separate them from the mud system via the mud cleaning equipment. They lead to severe gelling of the mud and consequently high mud rheology and hole-swabbing tendency. This significant distortion in rheological properties of the mud was as a result of high solid content in the mud and possibly carbonate or bicarbonate. A dilution recipe was developed and applied to tackle both possibilities and the mud properties were restored.
Abandonment of wells is a significant part of oilfield abandonment, accompanied by abandonment of facilities and installations. Well abandonment operations in the Niger Delta of Nigeria have covered different categories of wells; –Previously suspended wells–Completed wells of varied completions design– single string, two string dual, two string multiple–Wells with varying degree of vandalisation including cases where entire wellhead system were cut off and stolen. Long term safety and prevention of reservoir wellbore fluids, or gas from being released to the environment, is a top priority. While well abandonment is subject to detailed planning from the early design stages for a well, external circumstances throughout the well life may pose new needs or challenges that need to be factored in and addressed when approaching the actual abandonment. For vandalised wells, their condition makes sub-surface abandonment objectives difficult to achieve. Compliance to desirable permanent barrier isolation strategy and legislation becomes technically more challenging. Dual string wells with tubing hangers severed off are difficult to handle. In wells with high deviation, loss of tension on the tubing due to the severed hanger can cause a permanent buckling in deeper sections, making it impossible to run in tools. Wells completed in multiple zones are faced with the risk of inter-zonal communication in the case where pressure regimes are significantly different, which could lead to more complicated sub-surface challenges. This also creates the risk of having combined loss and kick situation from two different reservoirs respectively. The increasing severity of vandalisation has re-inforced these risks and has increased the cost of abandonment significantly. This paper highlights the challenges and learnings from an abandonment campaign in the Niger Delta. The unique experience of abandonment operations on vandalised wells is detailed. A focus on further potential cost savings game changers hinged on efficient execution, competitive scoping and leveraging on technology is discussed.
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