Application of stratified sampling method in core plug sampling

The data obtained from reservoir core experiments are the basis of geological research, logging interpretation and oil and gas reservoir engineering calculations. The selection of a sample plug is the first step in a reservoir core experiment, and its sampling accuracy has an important effect on experiment results. When the sample number is limited, the conventional random sampling cannot meet the requirements of measurement accuracy. In view of the limitations of the traditional sampling methods, this paper described the principle of a stratified sampling method, and discussed its selection criteria. Based on measured data, the Monte Carlo algorithm was implemented using Visual Basic programming, and the measurement accuracy of random sampling and stratified sampling was compared. The results showed that, the data accuracy of stratified sampling was better than that of simple random sampling under the same sampling quantity. Therefore, according to the requirements of different experiments, a selection method of core plug samples based on stratified sampling was proposed. The method can estimate sampling accuracy and design a reasonable number of samples accordingly. When the number of experiment samples is limited, the sampling accuracy can be improved effectively.