Horizontal completions have changed considerably in the last few years in an effort to substantially improve the drainage of shale gas reservoirs. The spacing of fracture stages and perforation clusters are among the most crucial completion decisions that impact well productivity and EUR. Yet, the decision regarding stage spacing is rarely guided by an engineering process, as it remains a challenge to tie production performance and completion design. In this paper, we offer some insight on the impact of fracture spacing on the propagation direction of multiple transverse fractures, and consequently the expected performance of the horizontal well.Stress-shadow effects, related to the mechanical interference induced by a proppant-filled fracture, can cause fractures initiated from a horizontal well to deviate toward or away from previous fractures. A three-dimensional geomechanical model of the combined stress interference from multiple transverse fractures has been applied to typical wells in three shale gas reservoirs: Bakken, Barnett and Eagle Ford.The existence of an optimum spacing is demonstrated, where fracture stages remain transverse even when subject to stress-shadow effects. Below the optimum spacing, induced fractures may intersect previous fractures, and re-stimulate previously fractured regions of the reservoir, while leaving undrained portions of the reservoir un-stimulated. Such behavior is highly dependent on the mechanical properties of the shale, in particular the Young's modulus.Our modeling results suggest that the net fracturing pressure data measured in the field reflects the propagation direction of the fractures induced from the horizontal wellbore. A monotonic increase in net pressure, going from one stage to another, would indicate transverse fracture propagation during all stages. On the other hand, an up-and-down trend in the net pressure data is an indication that the mechanical stress interference is causing the later stage fractures to intersect fractures from previous stages. The net pressure data can, therefore, be used to investigate fracture-to-fracture interference and can be used to optimize the spacing of fracture stages in horizontal completions.

The products derived from thermal decomposition of NH 4 , K, and Na dawsonites have structural memory; that is, the original mineral structure in ammonium form (NH 4 AlCO 3 (OH) 2 ) is recovered upon treatment of the oxide in aqueous (NH 4 ) 2 CO 3 solution under mild conditions at pH ∼ 10. The memory effect holds in aluminas doped with transition metals such as chromium or iron. In contrast, treatment of calcined dawsonites in K 2 CO 3 and Na 2 CO 3 solutions leads to bayerite. The mechanism and kinetics of the reconstruction process were investigated by experiments in a parallel-reactor system varying treatment time, temperature, molar (NH 4 ) 2 CO 3 /Al 2 O 3 ratio, (NH 4 ) 2 CO 3 concentration, solvent, and dawsonite composition. The samples at different stages of the treatment in ammonium carbonate were characterized by X-ray diffraction, infrared spectroscopy, transmission and scanning electron microscopies, nitrogen adsorption, mercury intrusion porosimetry, and thermogravimetry. The reconstruction of the dawsonite structure from alumina follows a dissolution-precipitation mechanism and is accomplished in 10-30 min depending on the temperature. The transformation goes through an intermediate carbonate-containing aluminum hydroxide compound of amorphous nature followed by progressive dawsonite crystallization upon ammonium incorporation. In contrast with other families of materials having structural memory such as hydrotalcites, the original and reconstructed dawsonites present marked morphological and porosity differences. Upon reconstruction, nanoparticles in the as-made and calcined materials gradually transformed by way of complex intermediate morphologies into acicular nanoneedles with newly developed microporosity. The facile carbonation of alumina-related compounds in ammonium carbonate is potentially applicable for CO 2 mineralization.

A proppant-filled fracture induces mechanical stresses in the surrounding rock causing a reduction in the stress contrast and stress re-orientation around the open fracture. A three-dimensional geo-mechanical model is used to simulate the stress reorientation due to open fractures and generate the stress contrast contour maps. The reduction in stress contrast can lead to increased fracture complexity. This paper describes how fracture complexity can be increased by varying the completion design. In this paper, we identify the impact of operator-controllable variables in a completion design on fracture complexity. This can lead to more effective completion designs that improve well productivity, reservoir drainage and ultimately EUR. The possibility of greater fracture complexity and reduced effective fracture spacing and hence higher drainage area is demonstrated for an alternate fracturing sequence in comparison to the conventional fracturing sequence. The Young's modulus value of the shale and the in-situ horizontal stress contrast are shown to be significant factors controlling the extent of fracture complexity generated in a given reservoir. In addition, the effect of proppant mass injected per stage and the fluid rheology is also shown to significantly impact fracture complexity. We provide optimum ranges of fracture spacing, proppant volume and fluid rheologythe various formations analyzed. The use of these guidelines should result in more fracture complexity than would otherwise be observed. The results presented in the paper allow an operator to design completions and fracture treatments (rates, fluids, fracture spacing and sequencing) to maximize reservoir drainage and increase EURs. This will lead to more effective completion designs.