Induced fractures

Sudden but not total loss of fluid. It occurs often after trips (induced fractures) when heavy mud is in use. The loss zone is frequently below the deepest casing shoe. 

Flow in undisturbed rock normally is radial toward a site of lower pressure (the wellbore). The fracture crack created by high pressure injection usually forms perpendicular to the least principle stress that exists in the rock. The induced fracture intersects and disrupts the radial flow pattern such that flow becomes linear and more direct to the well. This phenomenon has been intensively examined and discussed by authors working in the discipline of rock mechanics as applied to hydrocarbon reservoirs. Hydraulic fractures created in oil and gas wells grow mainly vertically, parallel to the wellbore as depicted in Figure 1 and extend on either side of the perforated wellbore as "wings11 (7-11). 

Width assumes a great importance when one realizes that to maintain conductivity through the induced fracture it is nearly mandatory that the crack be filled with a solid spacing agent (called proppant) which will prevent the crack from closing completely after the hydraulic pressure on the well is released. 

Monta, N., Whitfill, D.L., and Wahl, H.A. "Stress Intensity Factor and Fracture Cross Sectional Shape Precictions From a 3 0 Model for Hydraulically Induced Fractures," SPE paper 14262, 1985 SPE Annual Technical Conference and Exhibition, Las Vegas, September 22 25. 

In order to develop such design criteria, one needs to study hydrogen-induced fractures in laboratory specimens that simulate the conditions in the fracture process zone in the actual pipeline environment in terms of the stress, strain, and hydrogen accumulation6 1. We have recently demonstrated6-9, that under hydrogen pressures up to 15 MPa both stress and hydrogen fields ahead... 

Taylor GN, Jee WSS, Christensen WR, et al. 1966. Thorium-228 induced fractures in beagles. Health Phys 12 889-893. 

Ch akoumakos, B. C., Murakami, T., Lumpkin, G. R. Ewing, R. C. 1987. Alpha-decay-induced fracturing in zircon the transition from the crystalline to the metamict state. Science, 236, 1556-1559. 

The concept involves the injection and detonation of a liquid chemical explosive in natural or previously induced fracture systems or the use of a pelletized explosive to enlarge and extend these fractures to provide fragmentation and interwell communication. This study is one of few known research efforts to evaluate results of detonating sheetlike layers of explosive to increase flow capacity in confined rock formations. The literature contained little information to guide the design of the experiments. Some related work, however, had been conducted by a few individuals and oil field service companies. Briefly, the earlier work resulted... 

Six shots (C, D, G, H, I, K) using approximately 1000 lb of TNT, were detonated in well 5 at depths ranging from 67 to 88 ft. The first three shots were not stemmed consequently, water and debris were blown to the atmosphere. The last three shots were sand tamped to the surface to fragment the maximum amount of oil shale around the wellbore and to permit the contained explosive gases to extend the induced fractures. 

Results of explosive fracturing tests in oil shale show that NG1 will detonate and that the explosion will propagate in water-filled natural fractures and sand-propped, hydraulically induced fractures in oil shale. The shale was fragmented by this method, and a successful underground retorting experiment to recover shale oil was performed. 

Most of the time, the three-point bending test (Fig. 12.2c) induces fracture without exhibiting yielding. The stress calculated here is a maximum stress due to the inhomogeneity of the stress field along the thickness ... 

Figure 14.5. Schematic of air-induced fracturing and extraction (from U.S. EPA, 1995c).

Accdg to Refs the USBurMines in cooperation with Sun Oil Co investigated the application of expl fracturing for stimulating natural gas recovery. Two tests con ducted in the shallow Buzzard Sand formation in Osage County,Oklahoma, demonstrated that desensitized NG can be safely loaded, displaced and detonated in hydraulically induced fractures both in open-hole intervals and thru casing perforations Refs l)W.D.Howell T.J.Clare, "Case... 

The influence of solvents has been touched on in Sect. 2.3.2. In fact, the influence of environment on crazing and fracture properties of polymers is of major importance in the practical uses of these materials. There are many ways for the environment to induce fracture by means of stress cracking, stress crazing, chain scission, chain crosslinking, etc. Therefore, environmental fracture has been widely studied, specially from the experimental point of view. Reference is a review of environmental cracking of polymers. Most work on environmental crazing has been done in liquid environments - (solvents and non solvents of the material), or high pressure gas environment, near condensation pressure (liquid nitro-... 

Escc does not appear to be a strong function of pH, but as the medium is made acidic, sensitized Type 304SS may fail in an intergranular mode at < scc (Fig. 10), probably due to the occurrence of a hydrogen-induced fracture process. 

Bayley TA, Harrison JE, Murray TM, Josse RG, Sturtridge W, Pritzker KP, Strauss A, Vieth R, Goodwin S. Fluoride-induced fractures relation to osteogenic effect. J Bone Miner Res 1990 5(Suppl l) S217-22. 

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