The W block in the south China sea is composed of thinly bedded sands and clays. The thickness of these sands varies from0.5 m to a few meters. Because the pressure and permeability also vary in each sand, the lamination has significant influence on the compartmentalization and productivity estimation.
The wellbore condition is moderately complex due to clay swelling and borehole collapse. It is of great importance to find a suite of technologies which can be usable under such challenging wellbore condition and acquire triple combo and pressure measurements.
Formation pressure while drilling (FPWD) was evaluated and used in Well A of W block. To moderate the influence of supercharging and obtain the best quality formation pressure, pumps-off pretest has been tried for first time in the south China sea which can take pretest while mud circulation stops and a battery provides the power. With the accurate formation pressure and mobility from FPWD, pressure gradients have been drawn that clearly illustrate the compartments along the well. Additionally, in a numerical simulator, by integrating the triple combo logging interpretation result and the FPWD pressure and mobility data, a single well productivity model has been established in this laminated reservoir to forecast the different production rate with different completion scenarios.
In a case study of proposed technology and workflow, in Well A, a total of 27 pretests have been taken while 23 of them are with pumps-off and the other 4 are with pumps-on. The pressure difference between pumps-off pretest and pumps-on pretest clearly demonstrated the data quality advantage of pumps-off option. Three oil gradients and one water gradient have addressed the two compartments in this well and the position of the oil-water contact. Different completion scenarios including different skin and downhole flowing pressure have been analyzed in the single well productivity model and defined the potential production rate.
