Forecasts for world energy demand project significant growth in heavy oil, which constitutes a large resource base to exploit. Estimated resources of unconventional oil (heavy oil, bitumen, oil sands, and oil shales) are claimed to be as much as 7 trillion bbl, with technical recoverable quantities varying from 1 to 3 trillion bbl. Because some of the heavy oils are too viscous to flow at reservoir conditions, special production technologies are required to facilitate flow from the reservoir to the wellhead, which equates to an increase in production and operating costs. Thus, exploration technology is of minor importance because large resources have already been discovered, so optimizing production technology is of greater importance.
Heavy oils are usually found at relatively shallow depths that are structurally faulted and in unconsolidated sands. This type of formation imposes lost-circulation problems during drilling and completion, especially during cementing. Because the common production method for heavy-oil resources is steam injection, full steam resistance and cement-sheath integrity up to the surface is desired. In Duri, Indonesia, conventional treatments with lost circulation material (LCM) pills and/or cement plugs before primary cementing have proven to be costly because of the associated rig time and materials. Moreover, most of these troublesome wells will have no cement returns to the surface during the cementing process, and, as a consequence, show poor bonding or even free pipe during evaluation.
A high-strength, low-density (HSLD) cement system was suggested for increasing primary cementing success in steam-injected, low-fracture-gradient areas. The hollow microsphere cement system is HSLD-acknowledged as a feasible solution because conventional cement designs lose to the formation. After optimizing a HSLD cement design in the lab with reliable results, execution was successful in addressing lost circulation in primary cementing, with even more reductions in remediation costs.
This paper presents a case-history study as well as the development background and process to obtain the optimum solution to overcome lost circulation during cementing in Duri, Indonesia, including optimizing a cement-job design using software, lab test results, a slurry design with economic analysis, and finally cement-bond evaluation results showing the added value for the operator from this initiative.