Untreated disposal of effluent water has the potential of scaling and plugging the in and near-wellbore regions. A case study and methodology adopted for the clean-out operation of water disposal well of Khurmala Field of Iraq is analyzed in the paper. Previous attempts of clean-out using high-pressure hydro- jetting tools along with acid treatment proved futile effort. As last resort, Fluidic Oscillator (SFO) was deployed for clean-out to regain access of TD and plugged fracture network before the eventual decision of work-over is made. Combination of SFO having pulsing, cavitation, and helix jetting action in conjunction with train of fluids consisting of diesel, 28% HCl and gel were utilized. The operational sequence of clean-out was in stages of 10m to clean 79m interval, comprising of slotted liner and open hole, filled with detritus. Low bottom pressure required a dynamic approach for treatment-fluid nitrification based on the success of clean-out and access to liner and open hole. Annular velocities required nitrification once the slotted liner and open hole were open for in-take. Rate of penetration, sequence and volume of fluid-trains, nitrification, and batch cycling were designed in accord to changing downhole dynamics during clean-out. A thorough investigation of detritus, designing of fluids, the accuracy of downhole hydraulics, and application of SFO proved to be an effective solution. It regained access to TD and connectivity between the wellbore and the injection zone. Injection increased from none to 15 bpm at 200 psi. The combination jetting effect of SFO (acoustic pulse (alike), cavitation, and helix) demonstrated to be more effective than rotating jetting tools. Moreover, the merits of operational efficiency supplanted conventional operations and environmental impacts were considerably low in terms of operating time, spent additives, and avoidance of work-over operation. The matching injection parameters post-operation with native parameters post-completion indicated that detritus is removed from wellbore and damage from the critical matrix is removed/bypassed. Currently, SFO is the only technology that has pulse, cavitation, and helix jetting structures. It has an effective jetting for in and near wellbore region while the kinetic energy transferred via fluid makes the impact stronger in the deeper region. The internal mechanism of the tool allows it to handle high pumping rate and pressures while external finishing offers multi-port orientation for outflow that allows targeting the fill in desired directions. The tool does not require redressing, thus it proves to be an efficient, safe, and cost-effective alternative
A case study is presented detailing the methodology used to perform the clean-out operation in a water disposal well of Khurmala Field, Kurdistan Region of Iraq. Untreated disposed water caused scaling and plugging in perforated liner and in the open hole that eventually ceased injection. Multiple attempts and investments were made in recent years to resume access to the injection zone using high-pressure hydro-jetting tools coupled with acid treatments. However, these attempts yielded futile efforts. Before proceeding with the decision of workover, it was decided to go for one final attempt to regain wellbore access using Fluidic Oscillator (SFO). Fluidic Oscillator (SFO) having pulsing, cavitation and helix jetting action was used in combination with a train of fluids consisting of diesel, 28% HCl and gel. The clean out was performed in stages of 10m, to clean the fill from 1091m to 1170m. Since the well bore was initially isolated from the injection zone, the cleanout was conducted with non-nitrified fluids. As the cleanout progressed and access to the liner and open hole was regained, the circulation of insoluble fill to surface required a lighter carrying fluid. Nitrification, volume of the fluids, batch cycling, and ROP were designed considering the downhole dynamic changes expected during each stage of the operation. The combination of SFO, the thorough selection of treatment fluids and the accurate downhole hydraulics simulations pertaining to different stages of the operation offered an effective solution and regained the connectivity between the wellbore and the injection zone. The injection rate of water increased from 0 bpm at 700 psi to 15 bpm at 200 psi. Throughout this operation, the SFO helix, cavitation, and acoustic pulse (alike) jetting proved to be more effective than other single acting rotating jetting tools. Also, Environmental impact was reduced by eliminating the need for a rig workover operation. The matching of the injection pressure when the well was first completed and the post job value indicated that the complete zone was exposed and scale deposits were removed from the critical matrix or bypassed. SFO has an effective jetting near wellbore region, while the kinetic energy transferred via fluid makes the impact stronger in the deeper region. Internal mechanism of the tool allows it to handle high pumping rate and pressures, external finishing offer multi-port orientation of outflow that allows targeting the fill in desired directions. Presently the SFO used in the case study is the only technology that has pulse, cavitation, and helix jetting structure. Also, since the tool does not require redressing, it proves to be an efficient, safe and cost effective alternative
The Gas Khuff well is an offshore appraisal well drilled to explore the potential of gas production from Khuff formation. The drilling objective of this well is to penetrate the top Khuff formation at 13877ft down to the lower Khuff formation at 16335 ft with 8 1/2 hole. It was vital to drill 26 inch hole section throughout depleted water aquifers and weak fractured limestone formations, down to the deepest possible depth (5639 ft). Moreover, the long-term integrity of the gas well necessitated cementing the 20 inch casing up to surface with low permeability, high compressive and tensile strength, and lightweight cement without the use of stage tool. Meeting these requirements shall provide long-term casing protection against corrosion, isolate sour water aquifers and reduce potential of gas migration in the future. Loss circulation problem encountered while drilling the 26 inch hole and large slurry volume exceeding the handling capacity of the rig and required to fill the annular space, were the main challenges in meeting these objectives. A combination of Novel light weight slurry mixed at 1.2 SG (10 PPG) and fiber were used minimize the potential of losses during the cementing job execution. Meanwhile, additional bulk storage, mixing equipment and pump unit were mobilized to the rig in order to double the bulk storage capacity and handle large volume of cement slurry. Introduction In the Gas Khuff well, the section of 5639 ft of 26 inch open hole was drilled across the several weak, water depleted limestone and cavernous formations, DAMAM, UMM ERADUMA, and SIMSIMA, that defy all cementing techniques since whatever is pumped is lost into formation vugs and fractures. During drilling, severe losses occur across the above mentioned zone. The well also passed through an intractable shale formation (Nahr Umr), which taking excessive volume of cement due to sloughing and caving. Casing point was reached with 60 bpm dynamic losses and 20 bpm static losses during drilling phase. Although total losses has been encountered prior cement placement. This new technique allowed covering the all open hole section with low density, and high compressive strength cement slurry. This helped also saving one day rig time by reducing the number of stages and cementing top up jobs. This light weight slurry system can be successfully used for intermediate casing where slurry design as low as 1.15 SG is needed. Also, it can successfully replace the two-stage cementing even if large slurry volume required. Lost Circulation Problem in Khuff well The loss of circulation during drilling or cementing operation is a serious problem usually resulting in inadequate zonal isolation. Loss circulation can occur in vuggy or cavernous formations, but most frequently the zones are highly fractured or loosely consolidated that are hydraulically parted at relatively low hydrostatic pressure. Lost circulation in Khuff well, can be described, using combination of two variables, first is the failure pressure of the formation (very weak zones), second is the placement pressure of the cementing operation. The first possibility is to improve the failure resistance of the formation by using bridging agents. The second possibility is to reduce the pressures involved in cementing placement, both dynamic and static. This can be accomplished by reducing the slurry density and or viscosity.
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