Descaling petroleum production tubing using multiple high-pressure nozzles

The mechanical approach of utilizing high-pressure water for scale removal has gained wider acceptance by multinational despite facing poor downhole performance challenges (cavitation) that need abrasion compensation (sand). Although sand particles have side effect of jeopardize the integrity of the well completion. Replacement of sand with stealing beads was excellent with good post descaling well completion integrity at the expense of environmental complexity. While the recent single nozzle, solid free aerated jetting descaling technique was characterised with poor scale coverage and high descaling time. This novel experimental scale removal technique utilises multiple high-pressure spray of up to10MPa and low flow rate of 12 l/m from multiple flat fan nozzles of different arrangement and stand-off distance. Housed in a constructed simulated production tubing chamber with vacuum and compression capacities to remove hard scale deposits of SrSO4 and CaCO3. In addition to the constructed wax deposit (paraffin) of different shapes signifying different growth stages of paraffin in production tubing. Generally, the performance of each or combination of the descaling parameters during the experiment depends on the shape and type of the scale deposit in question, most especially the chamber air concertation and nozzles arrangements. Also, the amount removed of all the respective scale deposit was found to increase with increase in injection pressure and reduction in number of nozzles. Likewise, the effect of stand-off distance toward the erosion rate of all the four respective descaling candidates was found to reduce with increase in downhole jetting position from 25mm to 50mm and 75mm, even though could be compensated with the right choice of nozzles arrangement. Injecting at 10 MPa with 5nozzles combination at ambient air concentration removed 49g, 32g, 3.2g & 1.8g of paraffin of hollow & solid shape, SrSO4 & CaCO3 deposits respectively, that cumulatively increases by a factor 1.6 after altering the nozzle configuration to 4nozzles. Subsequently reducing the numbers of nozzles to 3nozzles further increase the initial cumulative removal by a factor of 4.3 across the respective deposits at 25mm stand-off distance. Also utilising 3nozzles configuration at ambient chamber pressure removed 43g, 5.2g, 2g, & 1.7g of the respective deposits at 4.8 MPa injection pressure that cumulatively increased by a factor of 2 after throttling further to 6.0 MPa injection pressure. Further increasing the injection pressure to 10 MPa cumulatively increase the initial removal of the respective deposits by a factor of 7.2. While nozzle configuration (header arrangement) that depends on the size and shape of the sample, was found to remove 7% & 13% with CN arrangement more than CN and CNO configuration when descaling hollow shape scale at the best of other parameters in ambient condition. Whereas removing of solid, SrSO4 and CaCO3 deposit respectively, the CN arrangement removed 6%, 4% & 0.1%, more than the CNO arrangement and 0.08% & 0.1%, Varying the tubing air concentration from ambient to compressed and later vacuum was found to have direct impact on the resultant spray impact and aids erosion and hoops stress for the first condition. In addition to cyclin stress & abrasion for the second and cavitation jetting mechanism for the last air concentration. Likewise, 254g, 104g, 6.5g & 4.4g of the respective deposits was removed at ambient chamber pressure at optimised descaling parameters that as a result of introducing 0.2 MPa compressed air into the chamber increases by a factor of 1.5. Impressively, a better cumulative removal factor of 1.7 across all the respective deposits was archived after suction the chamber by -0.08 MPa. Prior to the descaling experiment some descaling preparational experiment of chemical and compositional analysis of the hard scale samples were conducted through the combination SEM, EDX and XRD and found to be CaCO3 & SrSO4 deposit respectively. While the constructed soft scale sample were confirmed to be paraffin through NMR & FITR analysis.