Fracture formation

The crown profile dictates the type of formation for which the bit is best suited. They include the round, parabolic, tapered and flat crown used in hard to extremely hard formations, medium to hard formations, soft formations and for fracturing formations or sidetracks and for kick-offs, respectively. 

Cone angles and throat depth dictate the bit best suited for stabilization. Cone angles are steep (60° to 70°), medium (80° to 90°), flat (100° to 120°), best suited for highly stable, stable and for fracturing formation, respectively. 

Treatments with Biocides Previously Fractured Formations... 

A special problem is the refracturing of a previously fractured formation that is contaminated with bacteria. In such a case the fracturing fluid must be mixed with an amount of biocide sufficient to reach and to kill the bacteria contained in the formation. The refracturing of the formation causes the bactericide to be distributed throughout the formation and to contact and kill bacteria contained therein [1181]. 

G. G. Geib. Hydrocarbon gelling compositions useful in fracturing formations. Patent US 6342468, 2002. 

Reiss, L.H. 1980. The Reservoir Engineering Aspects of Fractured Formations. Gulf Publishing, Houston, TX, p. 108. 

From the mechanical point of view, we are interested in the process of fracture formation and aperture. 

The stress-strain behaviour of the rock, including fracture formation, is a crucial component of the aperture changes. As mentioned before the deformation normal to the fracture is considered in equation (S) in order to obtain aperture changes. If an elastoplastic model is considered for the rock mass behaviour, fracture initiation can be associated with tension stresses. Fracture orientation is sensitive to the stress tensor orientation so the plane where the minimum principal stress (compression positive) occurs defines the plane of fracture formation. 

Could be used in broken and rich fracture formation without leakage. 

Reiss, L.H 1980. The reservoir engineering aspects of fractured formations. Gulf Publishing Company. 

Fig. 11.38 shows the density of the located AE events in projection to the three coordinate planes (x-y-plane at top, z-y-plane in the middle, and x-z-plane at bottom) in this as5munetric compression test as schematically shown in Fig. 11.39. The crack growth is illustrated in four stages (al to a4) of approximately 130 located events each and the final stage a5 of stress accumulation after the pre-fracture (290 events). The y-z-plane represents a view onto the macroscopic fracture plane, which is growing from top left to about 10 mm above the bottom surface. The x-y-plane shows that the contour lines of high event density coincide with the locus of maximum shear stress from finite element calculations. After the complete shear fracture formation the AE activity shifted to the remaining part of the specimen.

Fig. /. . Internal fracture formation and growth a.s the drawing length increases during wiredrawing.

The spectrum of metabolic bone diseases will result in a generalized weakness of bone thereby predisposing to pathological fracture formation. In rickets, due to a dietary deficiency of vitamin D, this can manifest as insufficiency fractures in the pelvis and long bones of the lower limb (Fig. 21.14). Advances in the management of chronic renal failure... 

In other words, the internal stress at the head of the pile-up, composed of n dislocations, is n times greater than the applied stress. As seen in later chapters, stress concentration plays an important role both in strain hardening and in brittle-fracture formation. The back stress of the pUe-up, Tb> acts on the source to create new dislocations. As long as ... 

The theory of bundle formation in the section Aggregation Prenomena in Solutions of Charged Polymers provides sizes, as well as electrostatic and elastic properties of ionomer bundles. The theory of water sorption and swelling, described in this section, gives a statistical distribution of pore size and local stress in pores. The merging point of both theories is a theory of fracture formation in charged polymer... 

In June 1992, Texaco announced the completion of a pioneering dual lateral horizontal well in a fractured formation in the Gulf of Mexico. A vertical well was drilled into the pay zone, at which point the drilling of two horizontal wells were initiated, heading in opposite directions. This example shows how the flow from such a completion is easily simulated. Fictitious input parameters are used for illustrative purposes. For brevity, the GEO files will not be shown. 

Bigelow, E. L. A Log-Inject-Log Application To Resolve Porosity in Tight, Fractured Formations, SPE Permian Basin Oil and Gas Recovery Conference, Midland, Texas, March 16-18,1994 (SPE 27644). 

The deeper the stimulation is, the lower will be the value of s. However, skin values less than approximately -5 are rare. Such negative skins exist only in wells with deep, conductive hydrauHc fractures (propped). Slightly negative skins may arise in frac-and-pack completions and in naturally fractured formations. If a well is neither damaged nor stimulated, then r = 0 (undamaged). 

In naturally fractured formations, an additional damage mechanism is the loss of whole mud deep into the formation. This form of damage is very difficult to remove entirely. Such damage may require hydraulic fracturing or repeated sequences of stimulation fluid injection and production, which is not always possible. 

HF reaction is controlled by surface reaction kinetics. HF reacts preferentially with high surface-area particles. It usually spends within a short distance from the wellbore if such minerals are abundant, which they usually are. Treatment typically does not exceed the wellbore by more than 1-2 ft (except in naturally fractured formations), and it can be much less. Nevertheless, removal of very near-wellbore formation damage can result in severalfold increases in well productivity, as indicated by the substantial reduction in productivity resulting from severe, very near-wellbore damage, as shown in table 4-1. 

There are occasions where treating above fracturing pressure may make sense—for example, in certain naturally fractured formations. There may also be certain sandstones (rare cases) in which acid etching is possible, similar to that achievable in carbonate formations. This is not necessarily a desirable effect in a sandstone. The formation would have to be competent enough to sustain or support a conductive channel. Acid etching is not a likely phenomenon to encounter in a sandstone and cannot be predicted with confidence. Nevertheless, it does bear consideration (at the least should be kept in the back of one s mind), especially with particularly hard rock. 

There are few cases requiring greater volumes of HF than 150-200 gal/ft. These are limited to high-permeability, high-quartz sands and fractured formations, such as shales, where high volumes of acid can open fracture networks deeper in the formation. Trending to simplified procedures enables use of higher HF volumes, when appropriate. 

The location of carbonate in matrix is important it may be possible to include HF in naturally fractured formations with high carbonate content. 

There are two basic types of acid treatments applicable to carbonates. They are characterized by injection rates and pressures. Acid treatment with injection rates below formation fracturing pressure is called matrix acidizing. Matrix acidizing is applicable only to formations exhibiting formation damage. There are exceptional cases— in particular, naturally fractured formations— in which acidizing at matrix rates in an undamaged carbonate formation may result in an acceptable stimulation response. 

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