The low invasion coring method was used to provide highly reliable connate water saturation in the Oligocene age, Lingshui III sandstone, Yacheng 13-1 reservoir, development Wells A1 and A2. Development well coring was implemented to resolve an uncertainty in the total gas-in-place.
A synthetic oilbase mud was designed to simultaneously operate at the 350°F wellbore temperature, provide reliable core connate water saturation, insure high quality well logs and minimize formation damage. The polyalphaolefin (PAO) synthetic base oil is biodegradable and is less damaging to the environment than diesel or mineral oil.
Procedures for obtaining a low invasion core in a remote location are described. Careful planning and execution are necessary for successfully obtaining low invasion core.
This is the first use of low invasion oilbase mud coring in China. Water saturations from cores are essential to accurately calculate the gas reserves. Possible gas-water contact variations cause uncertainty in connate water saturation from capillary pressure. Salinity variations in the reservoir complicate the calculation of connate water saturation from electrical logs. Accurate water saturation and salinity data from cores are needed to develop log models that can be applied in non-cored wells.