Prediction of Rock Strength using Drilling Data and Sonic Logs

Abstract

Uniaxial test (also called unconfined compression test) is one of most important tests used to measure rock strength. It is critical to obtain the rock strength parameters along the wellbore. Awareness of rock strength could better control drilling problems such as pipe sticking, tight hole, collapse, pack off and sand production. Rock strength also controls the drilling rate of penetration (ROP). The calculations of uniaxial Compressive Strength (UCS) are based on a simplified version of the ROP model proposed for tricone bits. The purpose of this research was to predict the uniaxial compressive strength based on sonic logs as a function of sonic travel and formation porosity. For obtaining continuous log strength along the wellbore in Ahwaz oilfield, quantitative relationships were developed between UCS and sonic travel time as well as UCS and both of sonic travel time and formation porosity. They actually are the outcome of regression analysis that resulting relationships are very practical and most often are specified by the researcher to the region of study. In this work, a larger well segment has been analyzed which there is no information break throughout the segment and it is investigated continuously. Using this approach, 3D model was a better predictor of uniaxial compressive strength than obtained equations related to transient time and results have also confirmed that the use of an recommended equations in this study can reduce drilling costs significantly.

An Improved Drilling Simulator for Operations, Research and Training

“…Such values of ROP_factor are well within the normal range one would expect which shows the validity of the approach. Similar results have been reported previously [12,14,15]. There is little discrepancy between predicted and actual ROP but this could easily be alleviated with further A second section from same Well_1 was taken, deeper, between 7380 ft and 10270 ft, consisting of only limestone and dolomite.…”

“…In order to predict UCS, the following equation was used based on available sonic data for the formations drilled [15],…”

Geomechanical model and wellbore stability analysis utilizing acoustic impedance and reflection coefficient in a carbonate reservoir

“…In geomechanical studies, the UCS parameter is determined based on equations and correlations made using studies on various rock types in different fields when is not available laboratory data of rock strength. Then, the relationship between UCS and various physical properties of rocks was investigated by well logs in these studies (Amani and Shahbazi 2013). In this analysis, Eq.…”