Manuscript Title: Characterization of Microannuli at the Cement-Casing Interface: Development of Methodology

Formation of microannuli at the interface of cement-casing can create well integrity issues. X-ray CT and Optical microscopy are technological trends that may have potential for direct visualization of microannuli. CT has an advantage of providing non-destructive visualization of microannuli, but its resolution suffers with increase in casing thickness. Conversely, Optical microscopy has the potential of providing higher resolution needed to detect smaller sized microannuli; however, information about microannuli is limited to only a few sections where samples have been sliced. The objective of the current article is to describe a methodology to examine the interface of cement-casing. Experimental work was combined with literature review. This includes both direct visualization methods, evaluation of current trends to better understand the characteristics and geometric variation of relevant leakage paths. We generate test specimens consisting of cement plugs, various steel casing thickness and nano-coated aluminium casings. Hydraulic sealability tests were conducted by injecting water at the cement-casing interface. Flow rates are then interpreted in terms of microannuli aperture and direct visualization of the cement plug-casing interface by CT and Optical microscopy was implemented. The experimental findings of this article will form a basis for studying geometry and size of microannuli as well as modelling of fluid migration.

Best Practices for Managing Subsea Well Plug and Abandonment Operation in Offshore Malaysia During COVID-19 Pandemic

In 2020, PCSB implemented the first permanent Plug & Abandonment (P&A) campaign for three Subsea wells in a gas field offshore Malaysia. The main objective of the campaign was to establish two (2) barriers for every movable hydrocarbon or overpressure bearing sand by placing laterally extended cement plug across impermeable formation with enough formation strength to handle the pressure of the formation to be isolated. The unique case of this operation was the challenges to execute PCSB's first subsea P&A operation in gas field Malaysia during pandemic situation. In March 2020, the Malaysian government imposed Movement Control Order (MCO) to curb the spread of the COVID-19. A semi-submersible rig was on-hired a week after government initiated the MCO, resulted in the rig preparation being badly hampered due to manpower management and material fabrication and delivery. PCSB was exposed to expensive rig daily rate that had to be managed. Four (4) main challenges were encountered during operation: safe protection for workers, expensive standby cost, manpower management and material fabrication and delivery. This paper, from the ‘project management’ point of view, describes the journey of managing rig operation during PCSB's first subsea wells P&A in Malaysia efficiently amidst the pandemic by reducing the impact of COVID-19 on project cost. With the experience of managing rig for subsea well operation, a complex operation in Malaysia, amidst pandemic, PCSB sharing on the experience is beneficial to provide context setting and benchmark on maintaining the efficiency of operation. Wells successfully met the objective of operation with no incident occurred, negotiated reduction on standby cost and managed to bring critical manpower on time during operation.

Optimisation of Plug and Abandonment Process Utilising Nuclear Technology for through Tubing Cement Evaluation

One of the major factors in the well plug and abandonment (P&A) process is to provide a proper isolation in aging wells which requires effective placement of the cement plug in the most suitable location in the well. Identifying cement placement is usually achieved by running cement evaluation logging to define the quality of cement and top of cement depth behind and in between the casing annuli. However, this comes with significant costs due to tubulars or casings removal requirement prior to logging run in order to conduct a proper evaluation. This is necessary since acoustic and ultrasonic based cement evaluation technologies will not be able to determine cement quality behind several casing layers if the job is done through tubing. The cost involved is substantial especially in offshore operation in which the daily operating rate is significantly higher compared to an onshore operation. A new approach to cement evaluation has been tested during the well P&A campaign in one of the aging oil fields in offshore, Peninsular Malaysia. A nuclear based technology comprised of Gamma-Gamma, Neutron-Neutron and Neutron-Gamma measurements were utilized to evaluate cement integrity behind production casing and between production casing as well as intermediate casing while logging run was deployed through tubing in memory mode. Log data was compared with acoustic and ultrasonic based cement evaluation technology that was deployed after the tubing was pulled out in one of the wells. Results had shown a consistent finding with the conventional ultrasonic based cement evaluation data. Based on the logging results, cement placement design and depth was finalized and the cement plug was successfully tested as outlined in the well P&A guideline. Findings from this logging run had provided useful insight to the operator to validate the nuclear based thru tubing cement evaluation technology for wells P&A application. Huge cost saving could be captured through this application as a result of eliminating total rig days via offline cement evaluation logging and based on the results obtained planning for the exact well P&A design requirement prior to the rig arrival. This paper will outline the method, tools used to acquire the cement evaluation data and its operational advantages. Acquired data will be presented and discussed along with the methodology used to determine cement volume and top of cement depth behind and in between the casings.

Managing Gas Well Blowouts: Case Studies from Assam-Arakan & Krishna-Godavari Basin

E&P activities are the early stage of energy production and pivotal for generating and sustaining economic growth. However, negligence and evaluating the circumstances incorrectly during these operations can lead to calamities like blowouts. This paper discusses two such tragedies, the Pasarlapudi (Krishna-Godavari) Gas Well Blowout of 1995 & Baghjan (Assam-Arakan) Oil Field Blowout of 2020, and provides possible well control measures and lessons learned. Pasarlapudi blowout incident occurred during the drilling operations. The pipe stuck-up situation at 2727m MD (Measured Depth) was detected by conducting a stretch test. Further analysis could include circulating brine, checking lost circulation and identifying casing leaks by measuring Sustained Casing Pressure (SCP), Operator-imposed Pressure (OIP), and Thermal-induced Pressure (TIP). Baghjan's gas well at the depth 3870m was producing at 2.8-3.5 MMSCFD. The aim was to plug the lower producing zone and recomplete the well in the upper Lakadong+Therria sand zone. Well was killed using brine, cement plug was placed and BOP installed. BOP was removed after the plug was set to begin the process of moving the workover rig. Well blew gas profusely during this process. Simulating a blowout and facing one, are two completely different situations. In Pasarlapudi's case, the well blew with an enormous gas pressure of 281.2 ± 0.5 kg/cm2. While drilling the production hole (8.5 inch), either differential pressure sticking, presence of water-swelling clay formation or the partial collapse of wellbore formation caused the pipe stuck-up situation. By conducting stretch test along with circulating brine, root cause of this problem could be identified. If differential sticking occurred, lost circulation could be checked & cured, while keeping the hole full. Circulating brine should solve the problem of swelling clay formation while formation collapse could have occurred due to the presence of plastic formation like salt domes. In the case of Baghjan gas well blowout during workover operations, probable safety measures could include placement of 2 or 3 backup cement plugs along with kill fluid or going for squeeze cementing before placing the cement plug & kill fluid while abandoning the lower producing zone. Attempts were made to bring the well under control by adequate water spraying, installing BOP. Water was pumped through the casing valve and a water reservoir was dug near the well plinth for the placement of pumps of 2500 gallon capacity. Proper safety measures should be used even when they're not the cheapest to avoid repetition of treatments and detrimental situations. SCP, OIP and TIP should be measured periodically whenever possible and the root cause of situations like lost circulation, pipe stuck-ups, kicks, casing leaks should be identified before proceeding towards drastic remedial operations. Innovations in countering well-control situations should be promoted invariably.

Delivered Successfully an Open Hole Side-Track from Very Challenging Formation Through Very Narrow MD Window: A Case Study from Kuwait

This article presents a unique case study where operating company, Kuwait Oil Company (KOC), decided to make an attempt to perform open hole side-track through a very narrow side-track window along with other exiting conditions such as severe downhole losses and drill through very challenging formation. To deliver such project in first attempt requires very detailed planning, close coordination with various service partners such as directional drilling and cementing. Placing a good side-track cement plug in such formation was a challenge, and 2nd challenge to get kicked off from this narrow window in first attempt which was the key. In case of failure, whip stock option has to be planned as a contingency, which possess new challenging of opening a depleted zone leading to commingling low/high pressure formation which could cause a complicated problem such as borehole stability, leads to stuck pipe problem. Failure to side-track from open hole could end of planning to drill extra hole which required extra casing string to run which will put this project well over AFE and heavily impact on well objective. This open hole Side-track was planned because while drilling original hole (12 ¼" hole section) close to planned well TD, experienced complete losses. In attempt to cure the losses, LCM was pumped with no success. Performed thixotropic cement plug job for losses control. While performing thixotropic cement plug job, the cement flash set before finishing the displacement, leading to stuck string. After backing off string and fishing attempts, unable to recover the fish completely. Fish left in hole leading to only 68 ft of open hole window available to side-track where performing a cement job was impossible due to severe losses. Only way to secure the well is to try for open hole side-track. With existing sever loss situation for initiating open hole side-track was a serious challenge due to lack of side force and flow restriction to initiate the side-track. Extensive pre-job planning, peer review and risk assessment was done in coordination with various service partners to deliver such challenging side-track. A hazard analysis decision tree was established to pinpoint the risks and appropriate mitigation measures along with contingency plan put in place. A detailed side-track guidelines was shared and review with the field crew. The wellbore was successfully side-tracked through a challenging reactive shale formation in a first attempt using a customized kick-off BHA, which not only helped to avoid loss zone in side-tracked hole but also provide additional cost savings to the company. The good hole condition at the side-track point was important to enable smooth passing of the following directional BHA to achieve directional goals.

Challenging Horizontal Well Abandoned with Innovative Plug Setting Technique and Tailored Slurry Design

Setting multiple plugs across a horizontal well can be a challenge. One way to do this is using the "pump and pull" methodology to achieve the objectives set out by the project team. Tailoring of the cement slurries and the execution of cementing operations for the successful deployment of multiple cement plugs using this method to achieve a dependable barrier across a horizontal reservoir section will be reviewed and discussed. A development well in Malaysia lost a bottom hole assembly (BHA) in their 8.5" hole section. This resulted in the requirement to abandon a long horizontal section along with the requirement to spot a 2,100 ft continuous cement plug on top of the BHA to abandon the well. The main challenge for setting a cement plug across a horizontal section, is cement slumping and stuck pipe, which might result in repeating cement plug jobs or non-productive time having a negative impact on well economics. To achieve isolation objectives in the first attempt, this long continual plug was broken up amongst four smaller individual plugs "stacked" on top of each other. The first 3 plugs were designed to each be 600 ft in length followed by a 340 ft plug. To avoid cement slumping, a cement support tool was deployed above the BHA before the first plug in the horizontal section. The first three plugs were placed in the horizontal open hole section and the fourth plug was placed at an inclination of 75 degrees, all using the "pump and pull" method. The pump and pull method is a common practice for worker operations with coil tubing and this similar technique can be applied in ERD drilling operations to aid in the homogeneous and accurate placement of cement plugs. However, for this job, the pump and pull placement method was preferred to aid in the homogenous and accurate placement of cement slurry through the horizontal open hole section. Detailed job calculations, the slurry design which was tailored for this application along with detailed operational procedures which resulted in the successful placement of all plugs on the first attempt under challenging well conditions will all be discussed. The approach utilized here resulted in the successful placement of a 2,100 ft continuous plug which isolated the BHA and saved the project valuable rig time. Similar approaches can be used in other areas to achieve successful results in first attempts to help well economics.

Precise Cement Displacement with a New Cement Plug Tracking Method

During the primary well cementing operation, when the cement slurry is pumped into the annulus around the outside of the casing string, it is very critical not to over displace and let the displacement fluid enter the annulus. Traditionally, to determine when to stop the cement displacement operation, the top cement plug position is tracked volumetrically by dividing the displaced volume by the casing internal cross-sectional area. However, the volumetric method is prone to uncertainties related to displacement fluid compressibility, high-pressure pump inefficiency, flowmeter inaccuracy, and variance in casing joint diameters. The new cost-effective cement displacement monitoring method is based on the analysis of the pressure pulses generated by the top cement plug passing the casing. These pressure pulses are detected by the standard pressure transducer installed at the cementing head. When correlated with the casing tally, these pulses identify the plug position related to the completion elements that provide better accuracy than the volumetric method used conventionally. The case studies include the successful cement displacement monitoring example and the case where the plug was prematurely stopped 90 meters above the landing collar, which was revealed by the subsequent drilling and confirmed independently by the new plug tracking method.

Making Workovers Easy and Cost Effective: Turning Old Ways into New Opportunities

A case study and methodology is presented to shed the light on the different processes followed during the placement of a non-damaging isolation barrier in a group of highly naturally-fractured and vugular gas wells. The temporary isolation aims at isolating the wellbore from the troublesome formation and allow the removal of the original completion string and install a new redesigned one. The process helped putting the wells back on production with-out the need to stimulate any of them. This helped client to reduce the overall workover cost by 40% and proved to be successful and efficient to complete the required operation in a time-efficient. The operator had 4 wells with OH sections ranging from 40-80m which were completed in the late 1990's with no production packer. To preserve wellbore integrity the completion string needed to be pulled and replaced by a string with production packer and DH gauges. Visco-Elastic Surfactant (VES) and calcium CaCO3 (carbonate) used ubiquitously in field operations were tested for optimal design to fill highly fractured OH without damaging formation. Caliper logs were not available, and the presence of natural fractures posed a challenge to calculate the actual OH volume. A system was developed to carry the CaCO3 into the wellbore in stages and slickline was employed to measure fill after each stage. Once the OH was filled with CaCO3 and well would support a fluid column coil tubing was used to place an acid-soluble cement plug in the short interval between casing shoe and end of tubing (6-9m). The paper describes the optimization process followed to tune the CaCO3 pads composition, gel composition, mixing and placement technique. The first well in the campaign required more than 10 times the theoretical volume of CaCO3 to fill the open hole with multiple settling issues at surface. It was concluded the surfactant gel was likely carrying the CaCO3 into the fractures. The procedure was modified to tie in a line of breaker solution to the well head allowing sufficient viscosity of the fluid to carry the CaCO3 from surface but immediately lose viscosity and allow the CaCO3 to settle in the open hole without being carried into the formation. Specific coil tubing procedures were employed to allow the setting of ultra-short acid soluble cement plugs (<6m). All wells were successfully isolated to allow the safe workover of the completion string and returned to production with no loss of gas flow, with-out the need to stimulate after the work over. The campaign exhibited a new method of employing existing technologies to achieve the objective in a highly challenging and relatively new oilfield of Kurdistan. The campaign also demonstrated the benefit, in terms of saving time and cost because of extensive pre-execution planning.

Successfully Abandoning Wells with Extreme Corrosive Environment Using Mechanical Aids – A Case Study from South Iraq

Well abandonment under a corrosive environment is often unpredictable and challenging, especially if the zone exhibits irregular wellbore geometry due to severe corrosion. These situations not only increase associated risks, but also greatly increase the abandonment cost for workover operation. This paper presents a successful application of a mechanical aid to replace a firm base using bridge plug or viscous pill base to abandon a well in the province of Basra in Southern Iraq. Numerous wells in Southern Iraq have compromised casing integrity due to sulphureous water flow from Umm Er-Radhuma / Tayarat formations, making their abandonment imperative. Due to unpredictable corrosion inside the casing, setting any type of mechanical bridge plug was a laborious operation, because the operator must run multiple logs to confirm the casing integrity and might not get the required casing integrity at the desired abandonment depth. Setting up a viscous pill was a challenge in the well environment, and in absence of a firm base it was highly probable that the cement plug would slump. Looking at multiple options to ensure the successful plug setting operation on the first attempt, it was decided to use a suitable mechanical aid, as a firm base to prevent the slumping motion of the fluids that were pumped to isolate sensitive zones. The unique foldable and adjustable parasol construction of the tool enabled it to be pumped through small diameter tubing avoiding any sticking, and it was a critical parameter for tool selection process. This paper summarizes the first-successful well abandonment using such a tool in the province of Basra in 7-in. casing and 9 5/8-in. casing. The logging tool was not able to detect one section of 9 5/8-in casing, which was presumably completely corroded. The first attempt to isolate it using a polymer system was not successful, since the fluid flowed to different leaks in the outer casing. The parted 7-in. casing made it impossible to identify the depth of lower leaks. Then a plan to utilize the mechanical aid was presented and subsequently approved. Tool was dropped and set above the top of 7-in. casing and gave support to the first cement plug to abandon the well, significantly reducing the time and cost of abandonment of the well by reducing repeated plug jobs. The use of the mechanical aid as a primary option to set plugs for abandonment purposes in corrosive environments has resulted in a great success by reducing non-productive time and enhancing zonal isolation results. Similar usages around the world will help in reducing workover operation economics where integrity of the casings is questionable.