For years the drilling industry has wrestled with the problems associated with well cementing. The introduction of pneumatic bulk systems increased cement slurry mixing rates but accurate density control still eluded the experts. Many companies have introduced process controlled mixing systems but these are both expensive and not totally reliable.
A new cementing system, that does not rely on bulking, has become available to the industry - a storable oilwell cement slurry that can be kept in a liquid state indefinitely and made to set as and when required.
Operators in Indonesia are now benefiting from this new technology. Slurries are mixed and tested to ensure they meet design specifications well before they are required on site. The "Base Slurry" or "Liquid Cement Premix" (LCP), which typically has a density of 16.0 pounds per gallon (ppg), is transported to the rig, diluted to produce the required density and pumped, ensuring a homogeneous slurry from start to finish.
Companies are being faced with environmental concerns throughout the world. This, and the requirement to reduce the size of drilling sites in environmentally sensitive areas, necessitated a change in the way these operations were serviced. Cementing companies historically have needed a large work area or "foot print" for bulking and mixing equipment.
Due to the staggering economic and population growth in Indonesia the government has undertaken an ambitious plan to supply sufficient electricity to support this development. An area crucial to the success of this plan is the use of the country's natural geothermal resource for electricity generation.
One of the many promising geothermal concessions earmarked in the plan is situated in a tea plantation on the island of Java. A drilling project was undertaken to evaluate and harness this excellent resource. The evaluation program incorporated the use of two slim-hole rigs to drill appraisal wells and establish the lull potential of the field.
With environmental and space constraints (Figure 1), not to mention the rigid slurry specifications required in geothermal cementing, an innovative solution had to be found. The use of LCP technology was introduced to fulfill these requirements - this paper is a case study of this novel solution.
Liquid Cement Premix (LCP) can be defined conceptually as a storable cement slurry that can be kept in a liquid state indefinitely and made to set as-and-when required. It consists of a premixed slurry of Portland cement (or other cementatious material) containing set retarding and conditioning agents, with water as the carrier fluid. This storable slurry can be tailored to have a storage life of anywhere from several days to over six months and it can be formulated with standard oilwell cements - API Classes G, H, C and A have all yielded satisfactory LCP's. It is also possible to prepare storable slurries based on blended cements e.g. with silica flour, flyash etc. When required, the LCP is activated, and/or otherwise modified as necessary, to yield a finished slurry with suitable properties for well cementing. This requires the use of an "activator", added immediately prior to pumping the slurry into the well. This "activator" reinitiates the chemical hydration and allows the slurry to set after a predetermined pumping time.
Properties of Liquid Cement Premix (LCP). Prior to activation the LCP essentially behaves as a weighted mud. It is stored as a slurry at a density of 16.0 ppg and is in the form of a stable suspension.
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