Theoretical Research And Engineering Application Of High-Pressure Gravel Packing

Loose sand reservoirs are suffering from sand production seriousely, which are distributed widely all around our country. Sand production problem can be found in many oil fields home and abroad and it is one of the important factor that confine the oil fields production increase. High pressure gravel packing is a popular sand control technology used by many oil fields at present. However, the theoretical system about high pressure gravel packing is not established effectively in a long period, disjunction of theory and practice, leads to the technology and construction parameters are not so reasonable, and the further development of high pressure gravel packing is blocked.The thesis analyzed the factors influencing the effect of high pressure gravel packing from the angle of the character of loose sand and the construction technology. Above this, the procedure of high pressure gravel packing could be described by the following words. Near well-bore area was compacted under grout pressure, elastoplastic deformation took place, and the gravels in carrier fluid filled the space, so the purpose for compacting and packing the near well-bore area was achieved. With the increasing of construction pressure, the stratum in the plastic area is compacted continuancely until carrier fluid could not be pushed into the space of the stratum, and the energy of carrier fluid gathered rapidly at this time, fractures emerging in certain directions when the pressure around aim stratum reached a certain degree.Based on the mechanics analysis of gravel moving in the carrier fluid, the thesis applies to the result of sediment movement, studied the migration mechanism of gravel during high pressure packing.Considering the fact that the configuration of near well-bore area after the construction was not understood rather clearly and the present mathematical model of frac-packing did not consider the near well-bore area might be compacted, firstly based on the Mohr-Coulomb criterion and the basic theory of plane strain axisymmetric problem, developed the relationship between the radius of compacted area and the stress, strain and displacement of near well-bore area, and the influence of rock parameters such as internal friction angel and young modulus was studied by some examples.On the basis of discrete element theory, numerical stimulation for loose sand reservoir was carried out by the software PFC2D, and some conclusions were attained. The results provided some recognitions about the near well-bore area configuration. The well bore had a uniform extension under uniform in-situ stress, the packed area was a proximate circle, the target stratum was compacted, and the porosity decreased significantly. It still had an extension under nonuniform in-situ stress, and the extension magnitude in the minimum stress direction was bigger compared with the maximum stress direction. In addition, different cementation strength made different near well-bore configuration after construction. The configuration of the loose sand reservoir with high cementation strength approximated to the low permeability reservoirs, but as to the weak consolidation reservoir, the rock near well bore was compacted with some fractures in the maximum stress direction.In order to determine the hardness of the stratum and provide theoretical guidance to high pressure gravel packing technology, rock compaction modulus was proposed creatively which was defined as the ratio of compression stress to compression strain under vertical restraint condition. On the basis of the deduction of compaction modulus, the concept of rock compressibility was put forward.With the deduced formulas, several oil wells offered by ShengLi oil field sandcontrol center with complete logging data were calculated. Two fitting formulas are attained according to some parameters such as compaction modulus, and some corrections to the fitting formulas were performed according to construction parameters and in-situ stress condition.Perforation section as the weak part of casing during high pressure gravel packing, was simulated through finite element method. With fixed perforation phase angel and density, the compressive strength decrease with the perforation diameter increase. With fixed perforation phase angel and diameter, the compressive strength decrease with the perforation density. With fixed perforation phase diameter and density, the casing stress increased with the perforation phase angel when the phase angel was located between 90 and 180 degree. Stress condition in the casing perforation improves when internal pressure is applied in the casing.An optimum design software for high pressure gravel packing was developed based on the theoretical model.