W.A.M. Wanniarachchi

Shale gas fracturing using foam-based fracturing fluid: a review

World energy resources are depleting at an alarming rate, and natural gas has been identified as an environmentally friendly energy resource, with shale gas being one option. However, the extremely low permeability of shale plays has caused them to fail to produce a commercially viable amount of gas. Therefore, appropriate production enhancement techniques, including hydro-fracturing, are required. This paper reviews the research on shale gas production enhancement using foam-based hydro-fracturing and focuses on research on shale deposit distribution around the world, the importance of shale gas recovery, major shale gas recovery enhancement techniques, the effectiveness of foam-based fracturing depending on the foam type used and the formation properties, advantages and limitations of foam-based fracturing compared to other fluids, and existing experimental and numerical studies and field studies. According to the available experimental and modelling studies on foam fracturing, N2-based foams are stronger than CO2-based foams. The effective viscosity that controls the foam rheology decreases with increasing temperature and decreasing pressure and foam quality, and fracture length reduces and fracture width increases with increasing foam quality. Although this technique has been tested in few shale plays worldwide, most studies have been performed in the USA and Canada. Therefore, the foam fracturing technique is still comparatively novel for other countries around the world.

Assessment of dynamic material properties of intact rocks using seismic wave attenuation: an experimental study

The mechanical properties of any substance are essential facts to understand its behaviour and make the maximum use of the particular substance. Rocks are indeed an important substance, as they are of significant use in the energy industry, specifically for fossil fuels and geothermal energy. Attenuation of seismic waves is a non-destructive technique to investigate mechanical properties of reservoir rocks under different conditions. The attenuation characteristics of five different rock types, siltstone, shale, Australian sandstone, Indian sandstone and granite, were investigated in the laboratory using ultrasonic and acoustic emission instruments in a frequency range of 0.1–1 MHz. The pulse transmission technique and spectral ratios were used to calculate the attenuation coefficient (α) and quality factor (Q) values for the five selected rock types for both primary (P) and secondary (S) waves, relative to the reference steel sample. For all the rock types, the attenuation coefficient was linearly proportional to the frequency of both the P and S waves. Interestingly, the attenuation coefficient of granite is more than 22% higher than that of siltstone, sandstone and shale for both P and S waves. The P and S wave velocities were calculated based on their recorded travel time, and these velocities were then used to calculate the dynamic mechanical properties including elastic modulus (E), bulk modulus (K), shear modulus (µ) and Poissons ratio (ν). The P and S wave velocities for the selected rock types varied in the ranges of 2.43–4.61 km s−1 and 1.43–2.41 km h−1, respectively. Furthermore, it was observed that the P wave velocity was always greater than the S wave velocity, and this confirmed the first arrival of P waves to the sensor. According to the experimental results, the dynamic E value is generally higher than the static E value obtained by unconfined compressive strength tests.