Various testing methods are used to assess the ability of new and in-service materi2t~ to resist hydrogen-sulfide cracking and to determine the effectiveness of anticorrosion measures. Stress is created in test specimens by constant deformation, constant loading, or a constam strain rate.The testing of specimens under constant deformation simulates corrosion cracking of structures subject to residual stresses. The indeterminacy and instability of the stress level in specimens, and significant duration and ambiguity are classed as disadvantages of these tests, since stress relaxation as a result of crack growth may slow, or even terminate crack propagation.Constant-load tests simulate corrosion cracking under operating stresses. Their advantage consists in the fact that the stress level is accurately defined, and the cross-sectional area of the specimen decreases with increasing corrosion cracking, and specimen failure will occur earlier than during constant-deformation tests with increasing mess.When tests are conducted by these methods, the tendency of the material to hydrogen sulfide cracking is, as a rule, determined by the lime to failure at a different previously adopted test base. These tests yield useful information; the results may, however, be deceptive, since the time to failure is summed from the incubation period, suberitical crack growth, and the time of complete fracture. A material possessing high crack stability (resistance to initiation of a corrosion crack) does not fail during the base test time as a result of which it may be classified as not inclined to hydrogen sulfide eraeidng, but may, in that ease, have low crack resistance, i.e., low resistance to the propagation of corrosion cracks. To ascertain this, it is necessary to subject specimens to prolonged testing; in the majority of eases, this is unacceptable from the practical standpoint, since it is difficult to hold steady the conditions under which the medium acts.To accelerate the tests, the composition or temperature of the corrosive medium is varied, and a notch is also applied to, or a preliminary crack created in the specimen. A disadvantage of these methods is their siL-~nifieant noncorrespondenee to the operating conditions of the structure; in that ease, only the crack resistance is determined, and the incubation period, which is the controlling period in hydrogen-sulfide-containln~ media, is excluded. Moreover, these methods cannot be used to investigate the effectiveness of various means of surface treatment to improve the stability of the test specimens.Many drawbacks of traditional methods of testing may be eliminated, using corrosion tests under a constant strain rate. This method of testing represents a variety of tension tests during which the specimen is tensioned in a corrosive medium at a constant strain rate to complete failure. The correlation between this method of testing and the practical situation is less obvious; under operating conditions and in all types of tests for hydrogen sulfide cracking, the suberitieal ...
This paper was selected for presentation by an SPE Committee following review information contained m an abstract submitted by author(sl. Contents of the pa.
One of the main causes impairing effective operation of gas wells is the appearance of stratal water during operation and its accumulation at the bottom which leads to increased hydraulic losses in the borebole, to unstable operation, and when the rock pressure in the deposit decreases considerably, cessation of operation altogether.To put wells into operation, traditional methods were used in the middle of the 1980s, in particular surfactants were pumped in, dispersion of the liquid at the bottom was applied, etc., but this did not bring about any substantial qualitative change in the operation of these wells.According to the recommendations of the branch institutes, the only method under the conditions of the Orenburg gascondensate field (GCF) enabling flooded wells to be operated is the compressor gaslift consisting in feeding the gaslift (the active) gas into the underpipe space of the well, and then through a valve into the pump--compressor pipe (PCP) of the lift, which ensures evacuation of the accumulating liquid into the loop of the well and its subsequent inclusion in operation.When this technology of putting wells into operation is used, the following circumstances have to be taken into account: the active gas that is used is purified gas supplied to the UKPG for technological purposes from the Orenburg gasscrubbing plant (GSP) under a pressure of 4 MPa; the product from the well is highly toxic (H2S, CO 2, mercaptaus), so far ecological reasons the gas therefore cannot be pumped off into a special tank (storage vessel); the product of wells with a considerable volume of water is received on a fiat c, ~ the UKPG which requires separating equipment with the necessary productivity, and also the corresponding responsiveness of the absorbing wells.Let us consider the possibilities of using compressor installations for putting into operation flooded wells on the example of the UKPG-2 where the mass flooding of the wells requires the given technology to be introduced.Stratal water appeared in the product from the wells of the Orenburg GCF almost from the first years of development of the wells, and already in 1996 the daily volume of the extracted water was 3291 m 3. The zone UKPG-2, whose specific weight in the total gas output amounts to more than 15%, is actively flooded in the process of vigorous development. The mean daily removal of water attains 967 m 3, and more than half the available wells contain stratal water.The wells yielding stratal water are divided into categories in dependence on the degree of flooding. Table I presents the distribution according to categories of the flooded wells at the UKPG-2 at the beginning of 1996. From the point of view of the possibility of putting these wells into operation with the aid of compressor installations, the wells belonging to categories 2, 3, and 4 are of the greatest interest. The wells of these categories have a mean water yield of 23-24 m3/day, and their gas yield changes between 1000 and 25,000 m3/day.At the beginning of 1996 the rock pressure in the ...
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