Strength formation

If we consider a well trajectory from surface to total depth (TD) it is sensible to look at the shallow section and the intermediate and reservoir intervals separately. The shallow section, usually referred to as top hole consists of rather unconsolidated sediments, hence the formation strength is low and drilling parameters and equipment have to be selected accordingly. 

Medium Formation Bits. Medium and medium-hard formation bits are designed with more closely spaced teeth, since the bit cannot remove large pieces of the harder rock from the bottom of the borehole. The teeth also have slightly larger angles to withstand loads needed to exceed formation strength and produce chips. 

Rock Mechanical Properties. In the previous section (Figure 4-313), the wear of the bit teeth can be determined in shales by plotting the dimensionless bit torque (T, ) versus the dimensionless ROP (R,). By introducing a new parameter, namely the apparent formation strength, the bit effects can be separated from the lithology effects. 

Figure 4-318. Schematic plot of the dimensionless torque T, versus he apparent formation strength...

Compute the drilling formation strength (FORS) and plot versus depth. 

Figure 4-323. Formation strength versus depth (a) grid (b) plot of calculated values.

Figure 4-335. Computations of the formation pressure, lithology, and fluid content made with MWD formation-strength, LWD resistivity, gamma ray, neutron, and density measurements. (Courtesy Anadrill [113].,)...

The grout pattern is shown in Fig. 19.17b. The thickness of the grout ring surrounding the tunnel varied between 3 and 6 tunnel diameters, depending on the upgrouted formation strength. 

The complexation equilibrium (11.2) corresponds to an equilibrium constant K given by formula (11.3) this measure of complex-formation strength is called the stability constant. 

For the types of predictions described by Veeken et al. (24) and Morita et al. (45, 46) to be effective, formation strength, from actual measurements or log based correlations, is required. 

A new sidetrack was thus planned. This was the second time the plans for the well had to be changed and it was now planned to use managed pressure drilling (MPD) because of new information about pressure eonditions. Extensive tests of the formation strength showed that the pressure toleranee for further drilling was redueed. MPD involves extra pressure on light mud so that it is possible to regulate the pressure in the well at any time. 

Novitsky, Y.W., Harrell, A.G., Ciistiano, J.A., Paton, B.L., Norton, H.J., Peindl, R.D., Kercher, K.W., Heniford, B.T. Comparative evaluation of adhesion formation, strength of ingrowth, and textile properties of prosthetic meshes after long-term intra-abdominal implantation in a rabbit. J. Surg. Res. 140(1), 6-11 (2007)... 

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