Construction of synthetic capillary pressure curves from the joint use of NMR log data and conventional well logs

Today, I read the paper ‘Construction of synthetic capillary pressure curves from the joint use of NMR log data and conventional well logs’ and find new ways to synthesize NMR bin porosities.

Summary

Synthesize capillary pressure curves in carbonate reservoirs from conventional and NMR logs by using a two-step approach:

1.     Simulate T2 (longitude relaxation time) distribution values

2.     The Pc values are predicted from CBPs through an inversion process

The correlation between capillary pressure and NMR T2 decay versus saturation data provides a methodology to derive synthetic capillary pressure curves.

Due to reasons such as complex pore type system, mineralogy changes, diagenetic overprints and variations in fluid content and saturation, it is hard for linear method for a sandstone reservoir to have an accurate estimate of pore-throat size and pore size distribution.

NMR T2 decay in porous media is described by equation: .

Assumptions:

(1)  Water-wet to mix-wet wettability

(2)  Lack of diffusion coupling

(3)  Compensation for hydrocarbon shift

,

In the fuzzy set theory, values have partial membership. A fuzzy inference system (FIS) is the process of formulating from a given input to an output using fuzzy logic.

Synthetic NMR log data and mercury injection Pc data were divided into 65% training sets to build the intelligent models and 35% testing sets for evaluating the reliability of the developed models.

As with the bin porosities, the TS-FIS and BP-NN models were employed to predict the Pc values.

The FL model with highest performance (small MSE) was chosen as the optimal model.

The comparison between measured and synthesized Pc curves is shown as follows:

This research shows the feasibility of the joint use of intelligent techniques and NMR log parameters (CBPs) to predict Pc-curves from conventional logs.

Intelligent systems could recognize the quantitative relationships between Pc and well logs data when NMR log and SCAL data are not available continuously throughout the reservoir interval.

Another use of the synthetic Pc data achieved in this study is to determine the Gas-Water Contact (GWC) and related information.

Tomorrow, I will read more papers and books on methods for pseudo NMR.