Content of PetroWiki is intended for personal use only and to supplement, not replace, engineering judgment. SPE disclaims any and all liability for your use of such content. In the context of fracturing, FIT stands for frac isolation tools. In the context of operations, FIT stands for formation integrity test.
Content of PetroWiki is intended for personal use only and to supplement, not replace, engineering judgment. SPE disclaims any and all liability for your use of such content. A sonic log that determines the top of the cement column and estimates the quality of the cement bond between the casing and the formation. Works on transmission of a sound wave and identifies areas that conduct the wave and those that do not (free pipe ringing). Communication is unlikely is CBL 5% of unbonded mv reading and bond length 10 ft (3 m).
A Formation Integrity Test (FIT) is a test of the strength and integrity of a new formation and it is the first step after drilling a casing shoe track. An accurate evaluation of a casing cement job and of the formation is extremely important during the drilling of a well and for subsequent work. Casing depths, well control options, formation fracture pressures, and limiting fluid weights may be based on this information. The main reasons for performing a formation integrity test are to: For a holistic view of the wellbore conducting FITs more often than is considered the industry norm can be helpful. Offset well information, geomechanics data, drilling fluid hydraulics, borehole imaging, and formation evaluation data lead to a competent wellbore, maintain stability, manage pore pressure, and optimize drilling, casing-running, and cementing operations.
Wu, Qian (The University of Texas at Austin) | Nair, Sriramya (The University of Texas at Austin) | van Oort, Eric (The University of Texas at Austin) | Guzik, Artur (Neubrex Co., Ltd) | Kishida, Kinzo (Neubrex Co., Ltd)
A good cement-casing bond is essential for effective zonal isolation in both active and abandoned wells. A new method was developed to monitor the cement-casing bond in real-time and in-situ using a fiber optic distributed temperature and strain sensing (DTSS) system. To demonstrate the concept, the DTSS system was used in a laboratory-scale well model, which has a fiber optic cable installed helically on the outside surface of a steel pipe that served as a model for a casing string. A cement annulus was created by placing the steel pipe with the optical fiber into a larger PVC pipe. The DTSS system successfully captured strain changes at the cement-casing bond due to an axial load applied on the casing. The helical wrapping installation enabled circumferential measurements of temperature and strain changes in the entire cement annulus. The results were used to evaluate the risk of cement debonding by estimating the shear stress in the fiber and by comparing it to the shear strength of the cement bond. In addition, the effect of embedding a fiber optic cable on the hydraulic integrity of cement annulus was also evaluated using a gas permeability test. The permeability of cement samples with embedded fibers was found to be elevated compared to plain cement samples without fibers, but the permeability values were well within accepted industry limits. Compared to existing cement bond logging tools, the proposed fiber optic sensing system can provide continuous, real-time and in-situ monitoring of the cement bond and zonal isolation in either active or abandoned wells, without the need for wellbore entry. The system can serve as an early warning system to identify, and possibly prevent, the loss of a cement barrier, by providing detailed information (i.e. location, type, and severity of an event(s)) that will facilitate any remedial operations, if necessary.
Tang, Lik Jin (Sabah Shell Petroleum Co. Ltd) | Combe, Caroline (Sabah Shell Petroleum Co. Ltd) | Wee, Anson (Sabah Shell Petroleum Co. Ltd) | Mohd Radzi, Razif (Sarawak Shell Berhad) | Heu, Tieng Soon (Sarawak Shell Berhad) | Ho, Chen Nyap (Sabah Shell Petroleum Co. Ltd.) | Tan, Kenneth (Sabah Shell Petroleum Co. Ltd.)
Early during the M Field well design phase, it was realized that cementing would be challenging due to tight downhole pressure margins, S-shaped well trajectories with long horizontal section and the need to isolate more than one reservoir. Recognising that cement remediation would be both expensive and having low probability of success, a structured approach focusing on designing the cement jobs for success and getting it right the first time was adopted. Criteria on barrier requirements were agreed upfront by an integrated team consisting of Production Technologists, Well Fluid Engineers, Well Engineers, Petrophysicists, Technical Authorities and cementing contractors.
Early engagement allowed ample time for the team to agree on the mitigation measures for different cementing outcomes before the actual execution, thus avoiding potentially difficult decisions to be made on the fly. Cementing scorecards were populated with planned job parameters for each well. Mud removal and cement placement modelling was performed to get the optimal mud displacement to reduce the risk of channeling. If the modelling showed presence of channels and/or insufficient cement height, a re-design of the cement job was triggered. In the event that a satisfactory cement design cannot be achieved using the conventional methods, new technologies, such as dual stage cementing and managed pressure cementing, were implemented to increase the chances of getting good cement.
Once section target depth (TD) was reached, the scorecard and mud removal model were updated with the actual hole conditions. Adjustments in pumping rate, spacer and cement volumes and mud rheology were made to ensure an effective mud displacement and success cement job.
After pumping the cement, the scorecard and mud removal model were updated again and compared with the post job execution data such as theoretical top of cement (TTOC), lift pressure and pressure matching. Cement evaluation logs were obtained for the first three wells to calibrate the scorecard and mud removal model. For subsequent wells, cement evaluation logs were only carried as a contingency in the event that the theoretical top of cement did not meet the requirement. A cementing lookback was conducted post cement pumping and learnings were implemented for subsequent jobs. Over the drilling campaign, 18 casing strings were cemented and only two of those did not achieve the required top of cement height.
Designing the cement jobs for success and getting it right the first time provided significant cost saving on cement evaluation logging and on remediation while achieving the required lifecycle well integrity. This can only be achieved through a structured approach, early engagement and collaboration of an integrated and multidisciplinary team.