Publications

With the recent trend of developing depleted reservoirs to enhance hydrocarbon recovery, zonal isolation between layers of hydrocarbon bearing formations is becoming more critical and challenging. Depletion reduces the fracture gradient, hence imposing a need for light-weight cement systems. Often, the degree of depletion varies among different production intervals. Inadequate hydraulic isolation among them can lead to unwanted cross flow between the formation layers, leading to loss of production. Existence of high permeability sand layers complicate the isolation further since together with lower pore pressure they are conductive to fluid exchange to occur between formation fluids and the slurry water phase during and after slurry placement. Cement-formation interactions that occur from cement placement to cement setting will affect the quality of zonal isolation.Kurau field is located onshore, within the Padang Island of Malacca Strait Block. Several oil bearing zones are confirmed in the Lower Sihapas formation, which is characterized by sand layers with low formation pressures and high permeability. Despite following best cement placement practices and opting for high performance light- weight cement systems, previous cementing operations did not achieve satisfactory isolation across the targeted intervals.Further analysis revealed that the effects of cementformation interaction on the quality of zonal isolation need to be taken into account. Formation and cement interaction across the depleted and high permeability zones needed to be minimized. This required a modification of basic cementing practices and therefore a fully integrated approach for cementing production liners.Applying the lessons learned from the previous campaign, four production liners were cemented utilizing this integrated approach. The wells achieved proper zonal isolation and were considered a leap improvement over the previous wells.