Analysis of Cross Correlations Between Well Logs of Hydrocarbon Reservoirs

Abstract

We carry out a series of cross-correlation analysis of raw well-log data, in order to study the possible connection between natural gamma ray (GR) logs and other types of well logs, such as neutron porosity (NPHI), sonic transient time (denoted usually by DT), and bulk density (RHOB) of oil and gas reservoirs. Three distinct, but complementary, methods are used to analyze the cross correlations, namely, the multifractal detrended cross-correlation analysis (MF-DXA), the so-called Q cc (m) test in conjunction with the statistical test-the χ 2 (m) distribution-and the cross-wavelet transform (XWT) and wavelet coherency. The Q cc (m) test and MF-DXA are used to identify and quantify the strength of long-range cross correlations between the porosities derived based on the NPHI, DT, and RHOB logs on the one hand, and the GR log that is indicative of the presence of clay minerals in reservoir rocks, on the other hand. The Q cc (m) test describes qualitatively the presence of such cross correlations between the porosity and GR logs. Analysis by the MF-DXA method also indicates that the various porosity logs, the GR log, and the cross correlations between them are multifractal, hence confirming the long-range nature of the correlations. The results are confirmed further by the XWT, and indicate that the porosities estimated based on the NPHI logs are only weakly, if at all, affected by the natural GR radioactivity of reservoir rock and are, therefore, most reliable. The effect of length scale on the correlations and cross correlations 123 446 H. Dashtian et al. was studied in detail. It is shown that such correlations exist at all length scales, and that they are of multifractal type that must be characterized by a spectrum of exponents.

Spatial analysis of oil reservoirs using detrended fluctuation analysis of geophysical data

“…Indeed, small discrepancies are acceptable in statistical treatments. This last result is in agreement with Dashtian et al (2011a), who used cross-correlation analysis between well logs and found that sonic, porosity and density are more correlated between them than gamma ray.…”

“…In references Andrade et al (2009), Chun-Feng and, Gholamy et al (2008) and Tavares et al (2005), DFA is employed to interpret and filter images of seismograms. In references Ribeiro et al (2011), Lozada-Zumeta et al (2012, and Dashtian et al (2011a), this technique is used, as in this manuscript, in the analysis of well logs.…”

A comparison of methods for denoising of well test pressure data

“…As more information regarding the reservoir properties is collected, the uncertainty associated with the recovery of hydrocarbons decreased. Reservoir characteristics have long been studied by means of a variety of techniques such as well log data (Dashtian et al 2011), well test data (Braester and Zeitoun 1993;Vaferi et al 2011), seismic data (Arora and Tomar 2010), and well drilling data (Weber 1993). Among these methods, recording transient well pressures created by flow rate alteration is a useful measure to obtain reservoir properties (Athichanagorn and Horne 1995;Gringarten 1987;Sanni and Gringarten 2008;Vaferi and Eslamloueyan 2015).…”

Stratigraphic correlation of wells using discrete wavelet transform with fourier transform and multi-scale analysis

“…In the neural network based correlation techniques, the neurons are initially trained to identify a particular geologic marker for a given well and subsequently these are used to identify the markers in other wells. In the cross-correlation based well correlation techniques, the cross-correlation of raw well log data for corresponding logs between wells are done and a high correlation implies a correlation of strata (Dashtian et al 2011). The artificial intelligence based techniques suffer from the drawback that it is not able to identify gaps and stretching of sequences which probably might be due to the presence of uncorrelated strata.…”