Gravel Pack Evaluation Techniques to Ensure Sand Control in Deep Water Unconsolidated Gas Reservoir
Abstract: Effective sand control is extremely important for production of hydrocarbons from shallow unconsolidated sand reservoir. In absence of any sand control measure installed in the well, there is high risk of Sand production along with the hydrocarbons. Sand production may result in damage of X-Mass tree and/or Sub-sea infrastructure components. In extreme cases, when the sand production goes beyond the critical limit, it may lead to a situation when the field production has to be stopped. In view of this, in Deep… Show more
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Cited by 3 publications
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Many completions require some sort of pack to prevent fines migration associated with the high production rates necessary for economic recovery. Traditional evaluation of these pack completions has generally been accomplished using a combination of pressure analysis, material balance calculations, and basic logging information, often including the use of radioactive tracers. Radioactive tracers introduce significant hazards relating to health, safety, and the environment, and therefore are under strict regulations. This paper presents a new alternative pack-evaluation technology which eliminates these radioactivity-related issues. The new technique utilizes a recently introduced non-radioactive tracer containing a taggant material with a high thermal neutron capture cross-section. This tagged proppant can also be used as, or mixed with, conventional gravel or frac packing materials prior to downhole placement. The non-radioactive taggant is detected using standard pulsed neutron capture (PNC) logging tools, with detection based on the high thermal neutron absorptive properties and/or capture gamma ray spectral properties of the tagged pack material relative to other downhole constituents. The tagged pack material is indicated from: (1) changes in after-pack PNC detector count rates relative to corresponding before-pack count rates, (2) increases in PNC formation and borehole component capture cross-sections (Σfm and Σbh), and/or (3) increases in the computed elemental yield of the neutron-absorbing tag material, derived from the observed PNC capture gamma ray energy spectra. This technology has been successfully employed in induced fracturing operations in over 200 wells to determine fracture height, and in many situations also indicates relative fracture width. By further optimizing the concentration of the tag material in the proppant and the time windows utilized for PNC data processing for pack applications using Monte Carlo software (MCNP5), the resulting non-radioactive pack tracer (NRPT) technique can now not only evaluate gravel packs, but also fracture height behind the casing/gravel pack at the same time. Moreover, enhancements to this technique have also been developed to eliminate the before-pack log in some situations. As a result, these recent developments significantly simplify and shorten the logging procedure, and therefore reduce operational costs. This paper begins with a brief review of prior published MCNP5 modeling data on gravel pack and frac-pack evaluation, and then discusses recent additional modeling data utilized in NRPT taggant concentration optimization, utilizing the borehole geometry of the well in the field log example in the paper. The effectiveness of the new NRPT technology is then demonstrated with the field example, which has only after-pack logs. In the field log evaluation, the natural gamma ray log, silicon activation log, borehole sigma log, formation sigma log, and gadolinium (the NRPT taggant) yield log are all analyzed. The most suitable logs and log combinations for evaluating gravel pack and fracture height were identified based on the comprehensive analysis, and quantitative evaluations for gravel pack and fracture height were obtained. This new technique is especially useful in evaluating onshore and offshore pack completions where the issues and hazards associated with the use of radioactive tracers can be significant and in situations where periodic monitoring of the condition of the GP is important. Time monitoring is impossible with radioactive tracers due to the short half-lives of the tracers being used.
Many completions require some sort of pack to prevent fines migration associated with the high production rates necessary for economic recovery. Traditional evaluation of these pack completions has generally been accomplished using a combination of pressure analysis, material balance calculations, and basic logging information, often including the use of radioactive tracers. Radioactive tracers introduce significant hazards relating to health, safety, and the environment, and therefore are under strict regulations. This paper presents a new alternative pack-evaluation technology which eliminates these radioactivity-related issues. The new technique utilizes a recently introduced non-radioactive tracer containing a taggant material with a high thermal neutron capture cross-section. This tagged proppant can also be used as, or mixed with, conventional gravel or frac packing materials prior to downhole placement. The non-radioactive taggant is detected using standard pulsed neutron capture (PNC) logging tools, with detection based on the high thermal neutron absorptive properties and/or capture gamma ray spectral properties of the tagged pack material relative to other downhole constituents. The tagged pack material is indicated from: (1) changes in after-pack PNC detector count rates relative to corresponding before-pack count rates, (2) increases in PNC formation and borehole component capture cross-sections (Σfm and Σbh), and/or (3) increases in the computed elemental yield of the neutron-absorbing tag material, derived from the observed PNC capture gamma ray energy spectra. This technology has been successfully employed in induced fracturing operations in over 200 wells to determine fracture height, and in many situations also indicates relative fracture width. By further optimizing the concentration of the tag material in the proppant and the time windows utilized for PNC data processing for pack applications using Monte Carlo software (MCNP5), the resulting non-radioactive pack tracer (NRPT) technique can now not only evaluate gravel packs, but also fracture height behind the casing/gravel pack at the same time. Moreover, enhancements to this technique have also been developed to eliminate the before-pack log in some situations. As a result, these recent developments significantly simplify and shorten the logging procedure, and therefore reduce operational costs. This paper begins with a brief review of prior published MCNP5 modeling data on gravel pack and frac-pack evaluation, and then discusses recent additional modeling data utilized in NRPT taggant concentration optimization, utilizing the borehole geometry of the well in the field log example in the paper. The effectiveness of the new NRPT technology is then demonstrated with the field example, which has only after-pack logs. In the field log evaluation, the natural gamma ray log, silicon activation log, borehole sigma log, formation sigma log, and gadolinium (the NRPT taggant) yield log are all analyzed. The most suitable logs and log combinations for evaluating gravel pack and fracture height were identified based on the comprehensive analysis, and quantitative evaluations for gravel pack and fracture height were obtained. This new technique is especially useful in evaluating onshore and offshore pack completions where the issues and hazards associated with the use of radioactive tracers can be significant and in situations where periodic monitoring of the condition of the GP is important. Time monitoring is impossible with radioactive tracers due to the short half-lives of the tracers being used.
Hydrocarbon Saturation Evaluation Behind Gravel Packing and Complex Completion Through Advanced Pulsed Neutron Logging
Gravel packing in the annulus between the screen and casing ensures the production of reservoir fluids without sand production. However, the effectiveness for controlling sand production and the permeability of the pack decreases over the years. It is important to quantify the gravel packing together with formation fluids saturation evaluation for production enhancement opportunities. From pulsed neutron logging (PNL), analysis of the expanded set of elements and minerals at high accuracy allows the quantification of gravel packing and reservoir fluid saturation simultaneously. Between two PNL runs, the background gamma ray (GR) count is subtracted from the activated GR count. The gravel pack log is made from linear response between the good gravel section and the top of gravel or major void. Besides, from inelastic-capture measurements in gravel packs, the normalization of near detector inelastic silicon yield to the sum of silicon and iron yields is another effective gravel pack quality indicator. Later in the processing path for formation evaluation, different environmental corrections and elemental offsets are determined to remove the contribution of gravel pack, different borehole fluid, and casing and cement composition. Ultimately, the integrated interpretation of carbon-oxygen (C/O), Total Organic Carbon dry weight fraction (TOC), neutron porosity (TPHI) and fast neutron cross section (FNXS) enable accurate determination of formation gas, oil, water saturation condition behind gravel pack and casing. In three examples presented in this paper, the gravel pack (GP) quality has been addressed and analyzed based on two different methods: the traditional GR counts difference between activated and not log, and the direct estimate of gravel presence and percentage from raw elemental concentrations being measured by the advanced PNL simultaneously to the other pulsed neutron and carbon/oxygen measurements. Understanding the gravel packing and the contribution from borehole conditions will help to reduce the uncertainties of log response and to compute reliable rock petrophysical properties and fluids saturation in the formation. The prompt evaluation of these gravel pack logs can provide a more accurate understanding of borehole effects on the petrophysical answer. The information can also directly be used to determine the void in gravel pack completions. Further plan for void repair can reduce the formation damage resulting from fluid loss in the formation.
Recently a new non-radioactive tracer (NRT) technology has become available to locate proppant in induced fractures that offers a viable alternative to the prior technology which utilizes radioactive (R/A) tracers, thereby eliminating the environmental, safety, and regulatory concerns associated with the R/A materials. This new non-radioactive tracer technique also has application in evaluating gravel packs and frac packs. The new technology employs a non-radioactive ceramic proppant containing a high thermal neutron capture compound (HTNCC). This compound is inseparably incorporated into each ceramic proppant grain during manufacturing in sufficiently low concentration that it does not affect any proppant properties. This tagged proppant can also be used as, or mixed with, conventional gravel or frac packing materials prior to downhole placement. The NRT taggant is detected using standard pulsed neutron capture (PNC) logging tools, with detection based on the high thermal neutron absorptive properties and/or capture gamma ray spectral properties of the tagged pack material relative to other downhole constituents. The tagged pack material is indicated from:decreases in after-pack PNC detector count rates relative to corresponding before-pack count rates,increases in PNC formation and borehole component capture cross-sections (Sfm and Sbh), and/orincreases in the computed elemental yield of the neutron-absorbing tag material, derived from the observed PNC capture gamma ray energy spectra. In many frac-packing situations, combining Sfm and Sbh data permits identification of fracture height behind casing. In some applications, enhancements to these methods have also been developed to eliminate the requirement for the before-pack log. In this paper, log examples illustrate the effective detection of HTNCC tagged proppant placement in fractures and cement, and Monte Carlo modeling illustrates the viability of the detection/evaluation of gravel packs and frac packs using HTNCC tagged pack material. The modeling data and logs indicate the applicability of this effective, safe, and environmentally friendly logging technique to locate the placement of non-radioactively tagged downhole pack material in both gravel pack and frac pack evaluation.
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