Tag Archives: предел прочности
Wellbore stability is one of the major problems while drilling oil and gas wells. Shale, in turn, makes up about 75% of drilled formations, and over 70% of the borehole problems are related to shale instability  costing the industry, accordingly to conservative estimates, $700 million annually . As it was proven in several studies  the shale stability problem is related mainly to penetration of drilling fluid into laminations / fractures (between bedding planes and through the microfractures of shale) causing the mechanical failure and thus the loading of the well with cavings. In other words, the fluid invasion clearly weakens the shale making the shale stability very sensitive to the drilling fluid design. If the drilling fluid weight is too low, the risk of wellbore collapse increases. If drilling fluid weight is too high, drilling fluid invasion into these fractures and subsequent shale weakening makes the wellbore prone to instability. As a way to prevent or minimize the loss of wellbore stability the drilling fluid system includes proper bridging agents together with right drilling practices were proposed. At the same time it was noticed that shale in the same interval and formation reacts differently to drilling process. Some of them showing significant washouts and signs of instability and other stay stable and have in gauge hole. It has been suggested that stability of shale formations affected also by formation strength. And there are boundary values after which formations collapse and significant washouts occur. To prove this assumption the analysis of formation strength of shale was performed. The objective of this paper is to show the impact of formation strength to the stability of the wellbore in shale formations. The paper also provides the relation between thickness of layers and depth of washouts, and the boundary values of formation strength when shale loses the stability.
Analysis of the influence of fire-retardant coating on strenth properties of wooden building constructions
Russian and international experience in operation of buildings and facilities of different functional purpose, as well as the results of safety research show that operating companies, maintenance staff and supervisors should make ensuring the observance of fire safety requirements at construction sites a priority. The current fire codes classify building materials only in terms of fire hazard, so most of the modern fire-resistant materials for wooden building constructions are designed for reduction of fire hazard by limiting flame spread in case of fire. However, one of the criteria for fire-engineering classification of building constructions is their fire resistance degree. At the same time, the existing fire safety codes and standards apply this parameter for characterizing metal and reinforced concrete constructions only, which significantly limits the use of wooden constructions as load bearing ones. Therefore, it is appropriate to develop a flame retardant, which helps to raise the fire resistance of wooden building constructions in case of fire. Based on the analysis of the existing tools and methods for fire protection of wooden building construction elements, the authors chose the optimal ratio of intumescent coating components for wooden construction structures, application of which in conditions of a construction site is the most promising and effective method of wood material fire protection. The article considers the impact of the fire-retardant coating developed on strength properties of wooden building constructions. The results and methods of the tests conducted for determination of tensile strength of wooden structures after fire exposure are given. The developed fire-retarding composition of the paint helps to prevent decrease of tensile strength of wooden structures in case of fire, and, therefore, to keep their load bearing capacity. These results were achieved due to formation of porous coke framework at high temperatures on the surface of fireproofed samples, which helps to improve thermal-physical properties of the coating as a heat insulating material and increases dehydration period of the components in fire retardant paint and in the wood itself. The developed fire-retarding composition of the paint is harmful for execution of work on fire protection of wood structures of buildings and facilities of civil and industrial construction of the Republic of Bashkortostan.