American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc. Discussion of this paper is invited. Three copies of any discussion should be sent to the Society of Petroleum Engineers office. Such discussion may be presented at the above meeting and, with the paper, may be considered for publication in one of the two SPE magazines. Abstract This study has resulted in the development of four equations that may be used for the prediction of geopressure magnitudes from well prediction of geopressure magnitudes from well log and drilling parameter data. Equations are given for use with resistivity plots, conductivity plots, sonic travel-time plots, and corrected "d" exponent plots. All equations have the same theoretical basis. Introduction In 1965, Hottman and Johnson presented a method for predicting geopressure magnitudes by using resistivity and sonic log data. This technique has received wide acceptance even though the prediction charts were based only on data concerning Tertiary age sediments in the Gulf Coast area. It was specifically pointed out that these techniques were applicable only in areas where the generation of geopressures is primarily the result of compaction in response primarily the result of compaction in response to the stress of overburden. In 1972, this author presented a theory on the effect of overburden stress gradients n geopressure prediction techniques. Compaction caused by overburden stress was described classically in a soil mechanics book by Terzaghi and Peck in 1948. With a vessel containing a spring and a fluid, they simulated the compaction of clay that contained water. Overburden stress was simulated by a piston, as in Fig. 1. It was shown that the overburden stress, S, was supported by the stress in the spring, sigma, and the fluid pressure, p. Thus, the long-accepted equation of equilibrium was established. (1) S = + p If Fig. 1 and Eq. 1 are studied, it is obvious that if S is increased and the fluid is allowed to escape, sigma must increase while p remains as hydrostatic pressure. However, if the fluid cannot escape, p must also increase as S is increased. Hubbert and Rubey published a comprehensive treatment of this theory as related to sedimentary rock compaction. They showed that, as the overburden stress is increased as a result of burial, the porosity of a given rock is decreased. Therefore, some fluid that was once in the pores of a given formation was later squeezed out by compaction. In many such cases, there is no escape route for the fluid, and thus the fluid becomes overpressured according to Eq. 1. This happens in many areas, and such generated overpressured zones are often called "abnormal" pressure zones or "geopressure" zones.

In arriving at a new method of predicting formation fracture gradients, it was found that overburden load, Poisson's ratio for rocks, and pressure gradients vary with depth. Although the method was developed specifically for the Gulf Coast, it should be highly reliable for all areas, provided that the variables reflect the conditions in the specific area being considered. Introduction The subject of many discussions and technical papers in the last 20 years has been the prediction of the wellbore pressure gradients that are required to induce or extend fractures in subsurface formations. The subject merits this attention because of the frequently recurring problems that arise from an inability to predict fracture pressure gradients. predict fracture pressure gradients. Encountered in several common types of operations in the oil industry are problems associated with the prediction of formation fracture pressure gradients. When wells are being drilled in both new and old fields, lost circulation is often a very troublesome and expensive problem. Complete loss of circulation has been disastrous problem. Complete loss of circulation has been disastrous in some cases. Many times, such disasters could have been avoided if techniques for calculating fracture pressure gradient had been employed in the well plans, and if casing strings had been set, and mud weight plans had been followed accordingly. In areas of abnormally pressured formations, the prediction of fracture gradients during the well-planning stage is extremely important. In fact, it is as important as the prediction of formation pressure gradients, which has received a great deal of attention in recent years. There are several published methods used to determine fracture pressure gradients. However, none of these methods appears to be general enough to be used with much reliability in all areas. In 1957, Hubbert and Willis published a classical paper that included the development of an equation used to predict the fracture extension pressure gradient in areas of incipient normal faulting. Overburden stress gradient, formation pore pressure gradient and Poisson's ratio of rocks were the independent variables that were shown to control fracture pressure gradient, the dependent variable. In 1967, Matthews and Kelly published another fracture pressure gradient equation that is different from that of Hubbert and Willis in that a variable "matrix stress coefficient" concept was utilized. Later the same year, Costley wrote about a similar idea. Goldsmith and Wilson used a least-squares curve-fitting technique and field data from the Gulf Coast area to correlate fracture pressure gradient with formation pore pressure gradient and formation depth. They noted that the fracture pressure gradient increased with increasing depth while the pore pressure gradient remained constant. In each of these cases, the problem for which a solution was sought was to determine the bottom-hole pressure gradient required to initiate or extend a pressure gradient required to initiate or extend a fracture. Results of the previous work show that fracture pressure gradient is a function primarily of overburden stress gradient, pore pressure gradient, and the ratio of horizontal to vertical stress. There is argument for a fourth variable in that in many cases breakdown fracture pressure gradient is greater than the fracture extension pressure gradient. JPT P. 1353

This paper presents the resu[ts of an investigation ofIwo-phase, gas-liquid flow in horizontal pipelines. Experimental data were taken in three field-size, horizontal pipelines, two of which were constructed for this purpose. The data were obtained using water, distillate and crude oi! separately as the liquid phase, and natural gas as~he second phase. Experimental pressure-length traverse, liquid holdup and f?ow-pattern data were collected jor each set of flow rates, These data were used to deve[op three correlations that are presented herein. The liquid-ho[dup values correlated with various flu w parameters without regard to the existing flow pattern. The same was true for the energy-loss factors. A new flow-pattern map is presented that appears to be quire reliable, but not required for the pressure-loss calculations.The liquid-holdup correlation and /he energy-loss factor correlation are used in conjunction with a twe-phase flow power balance, developed during this study, to predict tite pressure bsses that occur during gas-iiquid f70w in horizontal pipelines. A recommended calctdational procedure is given, as weU as a statistical analysis of the results, This procedure lends itself to computer application, since several small pressure decremen [s are needed 10 calculate a pressure-length traverse. The correlations are shown graphically, but may be curve fitted with existing curve-f?tting computer programs,

Think of the money that could be put to better use if we could predict the depth below which commercial production will not be found. It has been suggested that the magic level in geopressured areas is where log resistivity ratios exceed 3.50. The theory offered here, with the hope that it will be carried further, is that the limiting ratio is a function also of overburden stress gradient. Introduction In 1965, Hottman and Johnson presented a method for predicting geopressure magnitudes by using resistivity predicting geopressure magnitudes by using resistivity and sonic log data. This technique has received wide acceptance even though the prediction charts were based only on data concerning Tertiary Age sediments in the Gulf Coast area. It was specifically pointed out that these techniques were applicable only in areas where the generation of geopressures is primarily the result of compaction in response to the stress of overburden. Compaction caused by overburden stress was described classically in a soil mechanics book by Terzaghi and Peck in 1948. With a vessel containing a spring and a fluid, they simulated the compaction of clay that contained water. Overburden stress was simulated by a piston, as in Fig. 1. It was shown that the overburden stress, S, was supported by the stress in the spring, and the fluid pressure, p. Thus, the long-accepted equation of equilibrium was p. Thus, the long-accepted equation of equilibrium was established. (1) S  =   +  p If Fig. 1 and Eq. 1 are studied, it is obvious that if S is increased and the fluid is allowed to escape, or must increase while p remains as hydrostatic pressure. However, if the fluid cannot escape, p must also increase as S is increased. Hubbert and Rubey published a comprehensive treatment of this theory as related to sedimentary rock compaction. They showed that as the overburden stress is increased as a result of burial, the porosity of a given rock is decreased. Therefore, some fluid that was once in the pores of a given formation was later squeezed out by compaction. In many such cases, there is no escape route for the fluid, and thus the fluid becomes overpressured according to Eq. 1. This happens in many areas, and such generated overpressured zones are often called "abnormal" pressure zones or "geopressure" zones. Hottman and Johnson recognized the main significance of the preceding theory and developed a very useful relationship between electrical log properties and geopressures. They reasoned that since rocks are more resistive to electrical current than is formation water, a well compacted shale containing less water (because the water has escaped) is more resistive than a less compacted shale containing more water (one in which the water has not escaped to the same degree). Also, they reasoned that a sequence of normally compacted sediments (in which water is free to escape) should have a normally increasing resistivity trend. They substantiated this when they plotted resistivities from actual well logs. Any resistivity decrease from the well established normal trend indicates the, presence of abnormally high-pressured zones. Empirical data from well tests and logs were used to develop a correlation of the pore pressure gradient as a function of the resistivity departure ratio (see Fig. 2). JPT P. 929

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