Monitoring and continuous reservoir evaluation is very important aspect of a well-planned Waterflood program. Valuable well and reservoir information needs to be obtained during the course of waterflood operation, which helps in determining oil recovery and decide on the future strategy of the Waterflood program. Keeping this in view, KOC decided to drill some observation wells completed with cemented fiberglass casing for monitoring the flood performance in sandstone and carbonate reservoirs in two different fields. The use of fiberglass casing facilitates the application of some deep induction logging tools for measuring the changes in formation properties behind the casing. Vital information such as oil saturation change during waterflood operation, vertical sweep efficiency and arrival time of different fluid fronts can be determined from these log surveys in fiberglass casing. Cemented fiberglass casing and liners were used over the years globally mainly for observation wells and in some cases for highly corrosive injection wells. However, the use of fiberglass tubulars as casing or liner needs careful planning for its safe deployment and longer life. The casing policy, depth, drilling mud weight and logging requirement mainly dictates the selection of a particular size and thickness of fiberglass casing. Special cementing program needs to be formulated due to its lesser strength properties (collapse, burst & axial rating) compared to normal steel casing. They can be run either as complete fiberglass casing/liner or as combination string with steel casing depending on the zone of interest and purpose of deployment. KOC has successfully deployed 9-5/8" size fiberglass casing as combination string with steel casing in more than 20 vertical/deviated observation wells. The depth of deployment ranges from 4500 ft. in sandstone formation to around 8000 ft. in carbonate formation. Additional care was taken while preparing/ planning the cementation to prevent failure of the fiberglass casing while cementing across deeper formations. This paper describes in detail the design and planning of the observation well completed with fiberglass casing. Different scenarios leading to selection of particular size of fiberglass casing supported by StressCheck application and cementing technique are presented. Some special consideration related to cementing and running in equipment, which needs careful attention. The paper with the deployment cases will be a quick guide to engineers.
Kuwait has an unconsolidated formation with viscous oil at shallow-depth. Drilling and completion of horizontal well at such shallow depth is quite challenging. Industry practice is to use Slant Rig for shallow wells. Drilling experts preferred solution that would not entail Slant Rig for any future interventions and instead suggested using conventional vertical rig to establish feasibility of drilling and completion as a pilot. Lots of pre-drilling studies were carried out which involved Geomechanics Study to understand Stress orientation, pore pressure and sanding risk; Laboratory test of return permeability on core plugs for drilling fluid design and pore-bridging material selection; XRD & SEM analysis for clay mineral identification; Torque and Drag Analysis for predicted performance during drilling and completion and Particle Size Analysis for sand control design with slotted liner. Pre-job coordination meetings, Daily briefings, usage of Rotary Steerable System, Geo-Steering and Mid-course correction of trajectory based on Real Time Data Monitoring resulted in well placement in sweet spot. Well by well, rig days got reduced, lateral lengths increased, tangent sections for pump placement optimised and practically no held up occurred during drilling, casing/liner lowering or completion. This was a World record of drilling horizontal well using vertical rig at such shallow depth. The well completion as verified from Silicon Activation log suggests optimal placement of the slotted liner. This is further vindicated from zero sand and water production, another great achievement for the pilot project. Till date 7 such shallow wells have been drilled with 6 on continuous production for over 2 years in different parts of the field. Successful drilling and completion of these shallow-depth horizontal wells by conventional vertical rig in an efficient and cost-effective manner has confirmed all the pre-drilling assumptions and technological tests for the pilot phase, reaching world record breaking achievement.
Sidetracking a preexisting drilled and cased wellbore poses numerous challenges. When sidetracking in an openhole environment, additional verifications of hole conditions are needed, which contribute additional unique challenges. In this type of wellbore, the operators must plan by selecting the sidetracking depth and then ensure that all the objectives are met from a well authorization for expenditure standpoint and geological target perspective. The quality of the openhole window or rathole is of immense concern to operators because this quality ensures that the bottomhole assemblies (BHAs) will pass through the rathole without difficulty. The openhole gauge must be confirmed because it can pose additional risks that might lead to costly multiple trips into the well to ensure that the rathole is in good condition. This paper presents a unique case study in which the operator, Kuwait Oil Company (KOC), was faced with the possibility of geological losses at the kickoff in the wellbore while attempting to sidetrack an existing wellbore. The operator contacted an oilfield services company and requested a unique technical solution to precisely sidetrack the wellbore in the difficult formation containing fractured dolomites, which are known to cause severe to complete losses. While drilling the 12.25-in. section, the BHA became stuck in the fractured dolomitic limestone formation. In this section, the operator had previously experienced severe to complete losses. Because fishing attempts to free the stuck BHA were not successful, the operator decided to sidetrack the wellbore in the open hole using an openhole whipstock. A casedhole sidetrack option was ruled out because reactive swelling shales with producing sands were located above the sidetrack depth; therefore, combining these zones was not practical because of the low-mud-weight limit required for drilling the fractured dolomite below the target depth. In addition, because only 70 ft of open hole existed between the 13.375-in. casing shoe and the stuck BHA in the hole, sidetracking with a cement plug was nearly impossible. The openhole wellbore was logged with a caliper to confirm the wellbore gauge. Prejob planning consisted of understanding the compressive rock strength from the offset wells to identify the lithological challenges unique to this application. A hazard analysis risk-control method was adopted to identify the risks and apply appropriate mitigation measures. An operating parameters plan was formulated by the engineering team and discussed with the operator and service company personnel and followed throughout the job. The wellbore was successfully sidetracked in the 12.25-in. section in a single run using an openhole whipstock, avoiding the loss zone, and resulting in additional cost savings to the operator. The condition of the sidetracked rathole enabled smooth passage of the directional BHA to meet the directional objectives. Furthermore, the openhole whipstock operation eliminated the need for multiple cement plugs in the sidetrack (in view of severe loss zones below) as well as the time required for drilling with a dedicated motor BHA for openhole sidetracking operation, saving the operator a minimum of 6 days of rig time. This operation was the first successful 12.25-in. openhole sidetrack operation in the Middle East, Asia-Pacific, and sub-Sahara Africa regions. As a result of this successful operation, the operator is proactively recommending the new solution across the entire KOC organization for wells with similar scenarios. By applying this unique and reliable openhole whipstock technical solution, the drilling team was able to deliver a successful well based on the original casing plan without any need for further sidetracks or changes to the wellbore casing design.
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