ALBERT

Description: Hydraulic fracturing treatment is one of the most efficient conventional matrix stimulation techniques currently utilized in the petroleum industry. However, due to the spatiotemporal complex nature of fracture propagation in a naturally- and often times systematically fractured media, the influence of natural fractures (NF) and in situ stresses on hydraulic fracture (HF) initiation and propagation within a reservoir during the hydrofracturing process remains an important issue. Over the past 50 years of advances in the understanding of HF–NF interactions, no comprehensive revision of the state of the knowledge exists. Here, we reviewed over 140 scientific articles on investigations of HF–NF interactions, published over the past 50 years. We highlight the most commonly observed HF–NF interactions and their implications for unconventional oil and gas production. Using observational and quantitative analyses, we find that numerical modeling and simulation is the most prominent method of approach, whereas there are less publications on the experimental approach, and analytical method is the least utilized approach. Further, we suggest how HF–NF interactions can be monitored in real time on the field during a pre-frac test. Lastly, based on the results of our literature review, we recommend promising areas of investigation that may provide more profound insights into HF–NF interactions in such a way that can be directly applied to the optimization of fracture-stimulation field operations.

Description: Highlights • Coupled geomicrobiology and geomechanics to investigate alterations in shales. • Microbial process can alter the mechanics, mineralogy, and microstructure of shales. • Biogeomechanical alterations reduced permeability by 93% and porosity by 38%. • Microfractures in shales can be sealed during biogeomechanical alterations. • Biogeomechanical alterations can enhance CO2 storage security and caprock integrity. Shales have been a major focus of the energy industry over the past few decades. Recently, there is a paradigm shift in the energy industry to low-carbon solutions, such as carbon capture and storage (CCS), to mitigate global warming caused by carbon footprint. The problem of long-term safe and efficient geological CO2 storage (GCS) and caprock integrity are some of the major challenges impeding large-scale CCS application. Here, we investigated how localized and bulk biogeomechanical alterations could potentially impact caprock integrity and CO2 storage in depleted shale reservoirs. We cultivated the shale core samples (containing both artificial-induced and pre-existing natural fractures) with a cultured microbial solution at specific temperature, time, and growth conditions. Subsequently, we obtain the properties of the fractured shale rock samples impacted by this microbial process. We investigate the impact of the mechanical responses due to the microbial process, on the long-term integrity and storage potentials of CO2 in shale reservoirs. Our results suggest that in Eagle Ford, Marcellus, and Niobrara shale formations, microbially-altered local and bulk mechanical properties can enhance the long-term caprock integrity and CO2 storage security by: (1.) Increasing the localized (+19% unconfined compressive strength, −20% Poisson’s ratio, +35% fracture toughness) and bulk (+50% unconfined compressive strength, −13% Poisson’s ratio) mechanical integrity; (2.) Decreasing permeability (−93%) and porosity (−38%); (3.) Altering the clay mineral content (−56%), calcite content (+21%), and morphology; (4.) Occluding microfractures; and (5.) Mitigating any potential leakage to the atmosphere through the caprock. This study considers the heterogeneity of shales, and provide valuable insights and viable assessment in solving the long-term GCS application in depleted hydrocarbon reservoirs.

Description: Highlights • Coupled microbiology and geomechanics to investigate alterations in shales. • Microbial process can alter the near-wellbore of shale gas reservoirs. • Microbial alterations of near-wellbore rock properties can weaken mechanical integrity. • Biogeomechanical alterations increased porosity (+42%) & permeability (+6430%). • Biogeomechanical alteration with other stimulation methods can improve gas recovery. Shale gas reservoirs, with typically ultra-low permeabilities, have been a major focus of hydrocarbon production over the past few decades. In this paper, we investigated how biogeomechanical alteration of near-wellbore properties could potentially impact hydrocarbon recovery from low-permeability reservoirs, using Wolfcamp shale and Niobrara shale formations. We first obtained the geomechanical properties using the scratch test method, in addition to the mineralogical, microstructural, and porosity and permeability measurements of the shale gas samples. Subsequently, we treated the core samples with a cultured microbial solution at distinct conditions. Further, we obtained the corresponding new geomechanical properties, in addition to the new mineralogical, microstructural, and porosity measurements of the samples impacted by the process. Finally, we showed the implications of the altered near-wellbore properties for hydrocarbon recovery from shale gas reservoirs. Our results suggest that in shale gas reservoirs, microbial-induced alterations of near well-bore properties could temporally reduce its mechanical integrity (Wolfcamp shale = −21% unconfined compressive strength, −42% scratch toughness; Niobrara shale = −24% unconfined compressive strength, −14% scratch toughness), increase porosity (+43%) and permeability (+6430%), and impact the microstructural and mineralogical properties. The near-wellbore biogeomechanical alterations could potentially improve hydrocarbon recovery by enhancing: (1.) the susceptibility for induced fractures to nucleate and propagate during reservoir-stimulation; (2.) flow pathways to improve hydrocarbon recovery.