Harvey Edwin Goodman

Formation Compressive Strength Estimates for Predicting Drillability and PDC Bit Selection

Various indirect measuring techniques are presently employed for estimating formation strength, which in turn is correlated to drillability and polycristalline diamond compact (PDC) bit selection. Formation mechanical properties derived from conventional open-hole logs in combination with a rigorous assessment of formation shear wave velocities can be used successfully to determine drillability as it pertains to bit selection. Formation drillability is best determined from unconfined compressive strength and the angle of internal friction assessment. Rock strength is found to correlate well with the overall measures of bit effectiveness. Further, that angle of internal friction, which is a subsidiary rock strength parameter, correlates with PDC bit wear rates. Compressive strength and drillability have been linked in the laboratory and observed in the field since the early 1960s. Compressive strengths, however, need to be qualified as a function of confinement stress. The concept that compressive strength increases with confinement stress is well-understood and can be easily explained with Mohrs failure criteria. With the Mohrs failure technique, it is important to understand that inherent rock strength properties (cohesion and angle of internal friction) must be known before compressive strengths can be estimated. This paper also presents case histories from Gulf of Mexico wells that illustrate how unconfined compressive strength and angle of internal friction can be employed to indicate drillability as it pertains to optimized bit selection.

Propagation of a finite-amplitude elastic pulse in a bar of Berea sandstone: A detailed look at the mechanisms of classical nonlinearity, hysteresis, and nonequilibrium dynamics: Nonlinear propagation of elastic pulse

We study the propagation of a finite-amplitude elastic pulse in a long thin bar of Berea sandstone. In previous work, this type of experiment has been conducted to quantify classical nonlinearity, based on the amplitude growth of the second harmonic as a function of propagation distance. To greatly expand on that early work, a non-contact scanning 3D laser Doppler vibrometer was used to track the evolution of the axial component of the particle velocity over the entire surface of the bar as functions of the propagation distance and source amplitude. With these new measurements, the combined effects of classical nonlinearity, hysteresis, and nonequilibrium dynamics have all been measured simultaneously. We show that the numerical resolution of the 1D wave equation with terms for classical nonlinearity and attenuation accurately captures the spectral features of the waves up to the second harmonic. However, for higher harmonics the spectral content is shown to be strongly influenced by hysteresis. This work also shows data which not only quantifies classical nonlinearity but also the nonequilibrium dynamics based on the relative change in the arrival time of the elastic pulse as a function of strain and distance from the source. Finally, a comparison is made to a resonant bar measurement, a reference experiment used to quantify nonequilibrium dynamics, based on the relative shift of the resonance frequencies as a function of the maximum dynamic strain in the sample.

Changes in Near Wellbore Stress and Fracture Gradient Due to Cold Water Injection in a Sirte Basin Field, Libya

It is important to understand the effects of introducing thermal changes in the subsurface because such changes alter the state of stress and, ultimately, the behavior of the formation. Inducing fractures in the formation may cause injection fluids to advance at different rates through the reservoir, thereby reducing the areal sweep through the reservoir and the overall efficiency of a flooding operation. To avoid induced fractures, it is necessary to maintain water flooding operations below the fracturing (breakdown) pressure of the formation. For these reasons, it is extremely important to model the cold water injection response and to predict whether it is possible to inject without creating fractures in the formation. In late 2006 a reservoir simulation study using ECLIPSE was performed for 103N Field in Sirte Basin to evaluate the reservoir response to water flooding in an attempt to understand the potential for improving oil and gas recovery with water flooding. This study showed that the main effect of cold water injection on the recovery of N- Field was reduced injectivity due to high water viscosity. Another effect of cold water injection was that bypassed oil was cooled down and its mobility was reduced due to the increase in the oil viscosity, thus reducing ultimate recovery. This paper provides an extension of the reservoir simulation done by Wintershall to examine the effect of cold water injection on formation fracturing gradients. The work includes a review of the rock mechanics and stress analysis of the subsurface formations and provides an estimation of fracture penetration within the reservoir for a range of water injection rates and water surface temperatures. The conclusions of this study provide important insights into applying water flooding operations in the N-field.

Reconciling Subsurface Uncertainty With the Appropriate Well Design Using the Mechanical Earth Model (MEM) Approach

The involvement of the well engineer (WE) competency from the earliest phases of exploration is reaping economic benefit for major capital projects (single wells costing at least

Method for determining rock mechanical properties using electrical log data

25,000,000 US). As the geological and geophysical modeling work of the Explorationists matures and the subsurface picture becomes clearer, the appropriate well design flexibility is being achieved using Mechanical Earth Model (MEM) technology. This approach to well planning is particularly beneficial for deepwater exploration.