Lost circulation is considered a time-consuming, costly problem during the construction of oil and gas wells. There are several preventive techniques to mitigate this problem. Stress cage technology is a mechanical lost circulation method, in which the formation at the wellbore wall is strengthened to stop the creation of induced fractures as one of the main causes of lost circulation. In this research, a two-dimensional numerical model, considering the elastic, poro-elastic, and thermo-poro-elastic behavior of the rock, is built to investigate the effectiveness of the stress cage method. Results show that better performance of the technology is achieved if the fractures are bridged close to their apertures. Additionally, it was found that the difference between the elastic, poro-elastic, and thermo-poro-elastic models is slightly visible. The conclusion states that the application of the stress cage methods leads to an increase in hoop stress and subsequent formation fracture gradient.

Drilling fluids are a vital part of every successful well construction operation. Water based fluids are used commonly due to better environmental compatibility, lower cost and easier preparation. In offshore drilling, seawater can be used as the basis of water based fluids. Salinity of seawater restricts application of some additives. For example, bentonite settles in saline environments. In this study, a synthetic water is prepared based on Persian Gulf seawater. Bentonite, pre-hydrated bentonite and attapulgite suspensions were developed based on fresh water and prepared synthetic water. Rheological and filtration properties of fluids were tested to check their performance in synthetic seawater. Results of filtration measurements showed a thick mud cake and high filtration volume in pre-hydrated bentonite fluids. In the case of attapulgite, filtration volume of suspensions in synthetic water increased comparing to suspensions in fresh water. However, filtration properties were acceptable. Study on rheological properties revealed that Herschel-Bulkley model can predict rheological properties with a good accuracy. This is the case for suspensions in both fresh and seawaters. Also it was seen that all suspension had a flow behavior index less than 1, showing their shear thinning character. By increasing clay concentrations, higher consistency index, yield stress and gel strength values were reported. At higher clay concentration a stronger three-dimensional network of clay particles in aqueous environment and consequently a stronger gel structure were formed. Overall, it can be concluded that attapulgite can be used in the saline environment of Persian Gulf seawater.

Article is devoted to creation of new compositions of process solutions for lining of directional wells at high temperatures. Developed compositions provide high durability characteristics of cement stone. It is shown that with an increase in packing density of cementing slurry components durability characteristics increase and porosity and permeability of cement stone decrease, whereas an increase in temperature and pressure leads to a significant increase in compressive and bending durability, which is associated with presence of quartz in them. It has been established that introduction of special structure-forming additives to the composition of developed cementing solutions allows formation of sedimentation-resistant cement systems that can provide an increase in durability characteristics of cement stone and, in general, quality lining of directional wells. Study of rheological properties of developed cementing compositions showed that the systems have high yield strength at increased temperatures and pressures. Developed compositions of water-based spacer fluids increase the cleansing degree for both casing and rocks surfaces from mud and clay cake residues, which improves the cementing quality of oil and gas wells. Mechanism for increasing the washing ability of spacer fluids and durability characteristics of cement stone, depending on composition and properties of their constituent components, is disclosed.

The chemical and mechanical interactions between fluids and rocks, impairing the permeability and porosity of the reservoir, can lead to operational and economic challenges. These interactions can have a negative impact on the mechanical virtues of the rock, ultimately altering the petrophysical characteristics of the rock. The interactions cause alterations in the geometry of the pore space and the strength of the rock. Therefore, it is crucial to assess these variables before designing any oil recovery and gas storage project. The rock properties, particularly strength, permeability, and porosity, are changed during various stages such as drilling, production, and the injection of water or chemicals. In this regard, this research presents an examination review of the impact of fluid-rock interactions on the mechanical attributes of the formation rock, specifically focusing on the occurrence of formation damage. Generally, it is crucial to possess a strong comprehension of the interactions between fluids and rocks, as well as their effects on mechanical attributes and formation damage. This manuscript compiles recent studies to study the effect of interactions on rock petrophysical properties as well as mechanical properties, and in this regard, provides new perspectives on fluid-rock interactions in reservoirs. This understanding is vital in order to minimize both economic losses and technical complexities. Also, this manuscript can help researchers gain a complete perspective on the effect of fluids on rock mechanical properties in storage operations.

Over the last years, horizontal wells have found applications in many different geological and technical situations to enhance the production rate from the oil and gas reservoirs. However, well instability problems are often reported during construction of these types of wells. To mitigate instability problems, which are usually difficult and costly to solve, well stability analysis are conducted before the construction process begins. Different geomechanical and mathematical models that are used in the well stability studies, do not include the uncertainty assessments of the models. As majority of input parameters into the geomechanical models are subjected to some extent of errors and uncertainties, therefore, it is essential to quantify the uncertainty associated with the output of the geomechanical models. In this work, a Monte Carlo simulation technique is applied to quantify the uncertainty in the output of a poroelastic model to make more reliable decisions in the well construction process.