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Minimising Excess, Mitigating Losses and Improving Cementing Job Quality along Challenging Tophole Sections by a Simplified Novel Spacer-Cement Train: Evaluation of 3 Case Histories Offshore Malaysia


 The successful cementation of top-hole sections of three development wells offshore Malaysia has been very challenging since from offset wells nearby the fracture pressure in this section was very low. The section was supported only by an overburden of 328 ft (100 m) of water and 492 ft (150 m) of soil. With such low support, the tophole section had repeatedly hemorrhaged cement into the formation rather than getting good annular cement coverage to surface. As much as 130% more cement than should have been required was wasted in these efforts. In this study we review these case histories and describe how we overcame the given challenges by implementing an innovative spacer cement train.
 During drilling of the wells, the inadequate isolation had also allowed as much as 30 bbls/hr of drilling fluids to escape. Analysis suggested that a lighter-weight cement would reduce the pressure on the formation to levels the formation could support, enabling the annulus to be filled with cement without losses. To minimize the losses into the thief zone and to bring up the lead slurry to the desired depth by reducing the equivalent circulating density (ECD) at the top-hole a stable lightweight cementing system was engineered which does not require extenders or lightweight spheres. With this approach we simplified logistics and operations but also brought the quality control of the cementing system to a higher level, since the potential separation between dry-blended lightweight material and cement was no longer of concern.
 Laboratory testing was conducted to design this fit-for-purpose solution, which helped to eliminate the amount of synthetic products (such as beads) in the slurry, which greatly reduced its cost. At the same time, the solution provided better properties such as compressive strength development compared to the slurry that had been implemented on previous wells. A sealing spacer system was incorporated into the design to further prevent losses as an additional layer of assurance. As expected, the top-hole sections of the 3 wells were completed with no recorded losses. Cement coverage was confirmed throughout the annulus, and we did not have to pump 130% more cement than required, as we had to on previous wells.
 Unlike previously cemented wells in the area with low frac gradient along the top-hole section, the three wells that used the innovative spacer cement train did not suffer subsequent drilling fluids losses because they were adequately isolated. The combined effect of the lightweight cementing system and the sealing spacer was a drastically reduced cement cost and a better ultimate isolation.