This paper reviews the challenges faced during well cementing in the fields of East-North Kalimantan, Indonesia and describes utilizing an innovative cement spacer to successfully solve these issues. Unconsolidated formations and depleted reservoirs are main causes for lost circulation during drilling and cementing operations often resulting in poor cement bond logs and failed Top of Cement (TOC) requirements. The common practice to address these well integrity problems is to apply lost circulation material and low density cementing systems designed at 10.5 to 11.0 ppg. This strategy did not always accomplish the desired results and remedial cement squeeze jobs were needed for many primary cement jobs. To overcome these challenges, an innovative cement spacer system was engineered and successfully applied. The new environmentally friendly spacer system contains a biopolymer to mitigate loss circulation issues during cementing. It strengthens the wellbore wall by forming an effective seal along the formation, minimizing losses during cementing and preventing cement fall back after placement. The initial field application was immediately successful in obtaining full circulation returns during the cement job, a constant challenge on prior jobs. An added advantage was the cement slurry density could be increased from 10.5 up to 13.5 ppg without encountering any losses; despite exceeding the maximum theoretically allowable equivalent circulating density (ECD). As a consequence the increased slurry density improved early cement strength development which reduced wait-on-cement times and required using less concentration of expensive light weight cement materials. This, in turn, simplified operations and logistics and reduced costs. Case histories are presented covering more than sixty successful cement jobs using the new spacer system. Specific cases are discussed where: 1. successful results were achieved despite partial to total drilling related losses during the drilling phase, 2. cement bond logs have improved and 3. Remedial jobs have been eliminated. Conservative cost savings utilizing the new spacer design is more than $2.5 million USD. The product can be applied on high-temperature, high-permeability formations, those with low fracture gradients and fragile, unconsolidated, and fractured formations.
The placement of cement plugs in extended-reach drilling (ERD) wells is a challenging task. Poor hole cleaning, insufficient mud displacement, incomplete centralization, and tight ECD management are some of the more common risks. Mud displacement efficiency and accurate cement placement is notably more complicated in ERD wells due high deviation angles and asymmetrical fluid velocities; problems which are compounded in presence of Synthetic Based Mud (SBM). In fact, the industry standard for setting and successfully testing cement plugs in highly deviated wells is 2.4x per successful attempt. For deepwater projects, these risks must be mitigated to ensure timely operations as the financial implications of failed cement plugs are vast. Adopting best cementing practices in job planning and execution are beneficial elements to overcome the challenges; however even with excellent operational guidelines cement plug failures are common. A properly designed job should consider appropriate selection of equipment and materials, tailored properties of slurry and spacer systems, accurate down-hole pressure and temperature simulation, extensive laboratory testing, and identification and management of key risks. This paper will discuss the various operational, engineering, and unique design techniques for setting horizontal cement plugs in a SBM environment on a project in deep waters offshore Indonesia. To date, four kick off plugs have been set successfully in the first attempt on four consecutive ERD wells. Conservative cost savings for achieving first attempt kick-off is 1.2 MM USD, applying 12 hours per well (48 hours total) with a daily rig rate of 600K USD. The achievement is owing to application of best cementing practices in job design and execution, along with use of a unique cement system and innovative spacer. Techniques used in placing challenging kick off plugs are discussed followed by discussion on how the trouble-free operation has created value for both the client and service provider. Multiple case histories will be presented, along with specifics of the unique slurry and spacer system.
TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThe temperature difference between the wellbore drilling mud and the formation, especially in deep wells, causes volumetric expansion of pore fluid and rock matrix. Most existing models ignore the effect of convective heat transfer, which is a valid assumption for low permeability formations such as shales. However, convection plays an important role in controlling wellbore stability in high permeability formations such as sandstones.A 3-D thermo-poroelastic model that accounts for the effect of convective heat transfer is developed in this study. Transient coupled pore pressure and temperature equations for non-isothermal conditions are developed based on conservation laws. Thermal effects are generated by the temperature imbalance between the drilling fluid and drilled formations, and increase as the temperature imbalance increases. Cooling the formation is found to be helpful in lowering collapse pressure, resulting in a more stable borehole. However, it is also found that a formation is more vulnerable to fracture because cooling also lowers the breakdown pressure. A higher mud weight is required to fracture the formation when hot drilling fluid is used because hotter fluids increase the breakdown pressure. Also, a higher mud density is needed to prevent a wellbore from collapsing when a hotter fluid is being circulated through it.The model presented in this study is useful for wellbore stability analysis for deep wells and deep water applications where mud temperature varies significantly along the well path.
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