Clay-rich Reservoirs Research Articles

An experimental study of epoxy-based nanocomposite for chemical consolidation in a sandstone reservoir with high clay content

Sand production poses a substantial challenge in the oil and gas field, particularly in formations lacking the requisite strength to withstand pressure differentials during extraction. Many wells produce much less than their capacity due to the need to mitigate sand production and prevent well completion and wellhead erosion. The choice of sand control method depends on various factors, such as reservoir conditions, operational methods, and economic considerations, encompassing both mechanical and chemical approaches. In response to this challenge, this study investigates the application of a novel polymer nanofluid for chemical consolidation in clay-rich sandstone reservoirs, an area of exploration yet to be fully tapped. The research aims to assess the potential of polymer nanofluids as a promising solution for sand control in clay-rich reservoirs, with the overarching goal of bolstering well productivity and mitigating the adverse impacts of sand production. Conducted at a laboratory scale, the experiments involved the injection of 1 Pore Volume of consolidation fluid into sandstone cores with 15% and 30% clay content. Subsequently, the cores were subjected to reservoir temperature and pressure conditions for a period of 24 h. The obtained results show a significant enhancement in compressive strength, exceeding 700 psi, facilitated by the polymer nanofluid. Furthermore, permeability restoration reached approximately 89%, a notable improvement compared to preceding studies. Moreover, the introduction of foam injection rendered the core surface water-wet, suggesting potential advantages for reservoir management. These findings illuminate the promise of polymer nanofluids as an effective tool for sand control in clay-rich sandstone reservoirs.

Forecasting oil displacement in clay-rich reservoirs using water injection with varying mineral compositions

On the basis of a two-phase four-component fluid filtration model, mathematical modeling of a clay oil-bearing reservoir has been performed, which allows taking into account all physico-chemical processes occurring when exposed to water of various mineral composition, and on its basis to assess the possibility of restoring the reduced permeability of the reservoir due to the injection of water with low mineralization on the basis of treatment with a clay stabilizer. It has been established that the treatment of the layer with the optimal amount of clay stabilizer provides a significant intensification of oil production.

Effects of swelling-clay and surface roughness on the wettability of transitional shale

Wettability in unconventional reservoirs is poorly understood. However, it plays a fundamental role in fluid-rock interactions, and an understanding of wetting behavior is essential for capillary seal assessments and hydrocarbon reserve estimation and recovery in clay-rich reservoirs. In this study, the wetting behavior of transitional Shanxi-Taiyuan shale from the southern North China basin was examined via the contact angle (CA) and spontaneous imbibition (SI) measurement methods. Under water-air-shale conditions, water-wet and neutral-wet behaviors were observed, whereas neutral-wet and oil-wet behaviors were observed under water-oil-shale conditions (Young's equation was used to convert the water-air-shale system to the water-oil-shale system). When the CA method was used, the shale was shown to be hydrophobic, whereas when the SI test was used, the shale was observed to be hydrophilic. The water-air CAs are negatively correlated with the total organic content (TOC), carbonate and clay mineral contents (excluding those of illite). Furthermore, iron-containing compounds, such as pyrite and siderite, were shown to decrease the water wetness. A linear negative correlation was found between the surface roughness and the CA value. The relationship between these parameters can be used to predict the CAs at different surface roughness values for a given sample. The contradictory wetting behaviors between the results of SI and CA methods can be explained by: (i) differences between the CAs formed under water-air-shale conditions and those formed under hydrocarbon-brine-shale conditions; (ii) differences in the surface roughness, which is dependent on the texture and mineralogy of the shale sample; and (iii) clay swelling after water sorption and the formation of microfractures due to water–rock interactions.

An insight into a di-chain surfactant adsorption onto sandstone minerals under different salinity-temperature conditions: Chemical EOR applications

Surfactant flooding, a chemical enhanced oil recovery (EOR) technique, mainly aims at mobilizing the trapped residual oil by lowering the oil-water interfacial tension. The success of a surfactant flooding operation is strongly affected by surfactant loss through its adsorption on reservoir minerals. Therefore, the adsorption behavior of surfactants is of great importance and needs to be carefully investigated. The present study provides an insight into the adsorption behavior of a recently proposed surfactant, namely Aerosol-OT, on a number of minerals — including quartz-sand, kaolinite, illite, and montmorillonite — under different salinities and temperatures. The examination was carried out in the form of batch experiments, and the surface tension technique was implemented to determine the adsorption rate. The adsorption equilibrium data were examined through two adsorption isotherm models known as Langmuir and Freundlich. It was found that the adsorption rate increased with the increasing salinity, where the highest value was observed for kaolinite (21g/kg). However, an opposite trend occurred for temperature with the lowest adsorption rate (1.68g/kg) was obtained for quartz-sand at 85°C. The adsorption rate of Aerosol-OT was found to be higher than the conventional surfactants. A good correlation was seen between the equilibrium adsorption data and Langmuir isotherm model as their correlation coefficient (R2) exceeded 0.999. The results provide a useful tool to screen surfactants for the chemical EOR operation in clay-rich reservoirs.

Advances in grain-size, mineral, and pore-scale characterization of lithic and clay-rich reservoirs

Clay- and lithic-rich sandstones are difficult to characterize through uncored well sections in terms of their grain size, porosity, and mineralogy, all of which are required for assessing reservoir quality and production performance. This paper presents results from a study through one such interval and shows how a combination of different techniques can be used to better understand rock properties of complex reservoirs, thereby helping to reduce reservoir uncertainty. In this study, mean data from laser grain-size analysis are comparable to point-counted grain size, and both are considered as viable analytical methods. Automated quantitative evaluation of minerals by scanning electron microscopy (QEMSCAN®) provides a further useful and consistent grain-size measurement that can be applied to both core and cuttings samples. The QEMSCAN has also proved to be a valuable technique in the mineralogical analysis of sandstones that are lithic, clay- and feldspar-rich, eliminating the subjective nature that is inherent with optical analysis. Results from the studied interval show that porosity measured by conventional core analysis (CA) and mercury injection capillary pressure (MICP) analysis are generally comparable with log-derived total porosity. Porosity measured from point-counting and QEMSCAN techniques is significantly lower than total porosity, with the QEMSCAN porosity locally equivalent to log-derived effective porosity. Both point-count and QEMSCAN porosities show better correlations with permeability ( and 0.94, respectively) than total porosity values ( and 0.60 CA and MICP, respectively), suggesting that they might provide a measure of effective porosity in high-quality reservoir rocks.

An approach for methane hydrates reservoir dissociation in a marine setting, Krishna Godhavari Basin, east coast India

Gas hydrates are considered to be potential sources of clean energy. Various methods of gas hydrates extraction such as thermal stimulation, depressurization and inhibitor injection have been proposed, but each of them has some advantages and disadvantages depending upon reservoir conditions. This study deals with a production method applicable to the fine-grained clay-rich reservoir conditions in the Krishna–Godhavari (KG) Basin of India, by means of introducing an electrode into a gas hydrate reservoir to confine the energy delivery for dissociation and continue with depressurization for sustained production. The simulation of electrical heating using MATLAB and hydrate dissociation quantification using TOUGH + HYDRATE modeling programs, supported by laboratory studies, indicate that the reservoir temperature can be raised to 21.5 °C in one hour at a distance of 1 m from the electrode. Results indicate that 20.1 m3 of hydrate-bearing reservoir section with 90% hydrate saturation can be dissociated in 72 h at a given power of 90 kW. The energy balance calculations show that the energy supplied to produce is at the ratio of 1:3.5. To enhance the energy efficiency after 15 h of heating either the input power is increased in incremental stages or thermal stimulation is stopped and extraction is continued with the depressurization technique by pumping out dissociated freshwater from the zone of dissociation within the reservoir at a rate of 144 m3/h with a perforated borehole area of 2 m2 in the reservoir.

3D CSEM modeling and time-lapse sensitivity analysis for subsurface CO2 storage

Monitoring a time-lapse geophysical anomaly due to variation in the pore-fluid contents of a subsurface reservoir is critical for further development and management. However, it may be difficult to detect the changes in P-wave responses beyond a certain level of saturation. A comprehensive 3D finite-difference time domain (FDTD) forward modeling, based on idealized subsurface resistivity structures, demonstrates the possibility of marine controlled-source electromagnetic (CSEM) surveying to monitor the movement of subsurface [Formula: see text] storage. We focused on CSEM sensitivity studies with respect to variations in geometry and/or saturation of [Formula: see text] storage, evaluation of the effects of reservoir depths and lithology, and detection of [Formula: see text] leakage from the main storage. A 100% lateral expansion from the initial diameter (1500 m) of a typical [Formula: see text] plume with thickness and resistivity of 100 m and 80 Ωm, respectively, at 850 m below seafloor, results in 41% electric field (E-field) magnitude increase at 2500 m source-receiver offset for 0.5 Hz source frequency. In comparison, a 300% vertical expansion of a 50 m thick plume with diameter and resistivity of 2500 m and 80 Ωm, respectively, gives only a 7% E-field magnitude anomaly. An increase of the aspect ratio of a [Formula: see text] plume with diameter and thickness of 1750 and 130 m, respectively, by 110%, without volumetric change, results in a 20% E-field magnitude increase. The E-field magnitude differences due to [Formula: see text] saturation change by 20% in clay-rich (10% clay) and clean reservoirs are almost identical; thus, a time-lapse anomaly in a clay-rich reservoir might be detectable. A gradual inverse variation of offset and frequency can differentiate the responses of a 50 m thick shallow [Formula: see text] accumulation, 200 m below the seafloor, from the main [Formula: see text] plume at 850 m below the seafloor and allow for early warning of [Formula: see text] leakage.

Influence of releases from a fresh water reservoir on the hydrochemistry of the Tinto River (SW Spain)

The Tinto River is an extreme case of pollution by acid mine drainage (AMD), with pH values below 3 and high sulphate, metal and metalloid concentrations along its main course. This study evaluates the impact of releases from a freshwater reservoir on the Tinto River, identifying the metal transport mechanisms. This information is needed to understand the water quality evolution in the long term, and involves the comprehension of interactions between AMD sources, freshwaters, particulate matter and sediments. This work proposes a methodology for quantifying the proportions in which the different sources are contributing. The method is based on the mass balance of solutes and accounts for the uncertainty of end-members. The impact of the releases from the Corumbel Reservoir on the hydrochemistry of the Tinto River was significant, accounting up to a 92% of river discharge. These releases provoked a sharp decrease in dissolved metal concentrations, especially for Fe (approximately 1000 fold) due to dilution and precipitation. Cadmium, Zn, Cu, Co, Ni and Al suffered a dilution to a 12–16 fold decrease while Ca, Sr, Na, Pb and Si were less affected (2–4 folds decrease). However, these releases also gave rise to an increase in particulate transport, mainly Fe, As, Cr, Ba, Pb and Ti, due to sediment remobilisation and Fe precipitation. Aluminium, Li, K, Si, Al, Ni and Sr, together with Cu were present in the particulate phase during the discharge peak. The proposed 2-component mixing model revealed the existence of non-conservative behaviour for Al, Ca, Li, Mn, Ni and Si as a consequence of the interactions between the acidic Tinto waters and the clay-rich reservoir sediments during the bottom outlet opening. These results were improved by a 3-component mixing model, introducing a new end-member to account the chemical dissolution of clay-rich sediments by acidic Tinto waters.

Mechanical Alteration of Near-Wellbore Mineralogy for Improved Squeeze Performance

Summary Squeezing of clean, high-permeability reservoirs frequently results in relatively short treatment lifetimes because of the low inhibitoradsorption rates achieved. One of the main controls on inhibitor retention is near-wellbore mineralogy. Clay-rich reservoirs that contain abundant kaolinite, for example, often have long squeeze lifetimes because enhanced inhibitor adsorption can occur on the clay surface. The occurrence of calcium carbonate (CaCO3) cement in the near-wellbore region can also enhance inhibitor retention by forming a Ca2+/inhibitor complex. Previously published research (Fleming et al. 2009a) demonstrated the potential to mechanically alter the near-wellbore region through incorporation of low concentrations of kaolinite and organosilane. The data presented in the present work show that the additional incorporation of calcium carbonate provides a step change in the potential squeeze lifetimes achieved. This paper will present the results of using low, nondamaging concentrations of kaolinite and calcium carbonate particles in the preflush followed by scale inhibitor and organosilane in the main treatment. The kaolinite particles are retained in the near-wellbore region by the organosilane and enhance the number of potential sites for inhibitor adorption. At the same time, dissolution of the calcium carbonate particles by the acidic scale inhibitor forms a Ca2+/inhibitor complex that further enhances inhibitor retention. A review of the technology performance envelope has been made through coreflooding that includes optimizing the concentration of injection particles vs. permeability, the ratio of injected kaolinite to carbonate particles, and performance at elevated temperature (175°C) along with an assessment of how often a well would require retreatment with particles. The latter has involved successive coreflooding of the same plug with the full treatment package followed by brine flowback and retreatment with scale inhibitor alone or with organosilane. This information can be used by the assets in their evaluation on potential use of the technology.

The Effects of Steam Injection In a Sandstone Reservoir (Etchegoin Formation), Buena Vista Field, California

At Buena Vista field, California, 120 ft of post-steamflood core, spanning the middle Pliocene Wilhelm Member of the Etchegoin Formation, was taken to assess the influence of stratigraphy on light-oil steamflood (LOSF) processes and to determine what steam-rock reactions occurred and how these affected reservoir properties. High-quality steam (600F (300C)) had been injected ({approximately}1,700 psi) into mixed tidal flat and estuarine facies in an injector well located 55 ft from the cored well. Over a period of 20 months, steam rapidly channeled through a thin ({approximately}7 ft), relatively permeable (1-1,000 md), flaser-bedded sandstone unit. Conductive heating above this permeable unit produced, in the vicinity of the cored well, a 35-ft steam-swept zone (oil saturation = 0), overlain by a 29-ft steam-affected zone in which oil saturation had been reduced to 13%, far below the presteam saturation of 30%. Steam-induced alteration ('artificial diagenesis') of the clay-rich reservoir rock was recognized using SEM, petrography, and X-ray diffraction. Salient dissolution effects were the complete to partial removal of siliceous microfossils, Fe-dolomite, volcanic rock fragments, and labile heavy minerals. The artificial diagenetic effects are first encountered in the basal 6 ft of the 29-ft steam-affected zone. Based on the distribution of the authigenic phases,more » the authors conclude that the reactions took place, or were at least initiated, in the steam condensate bank ahead of the advancing steam front. Although these changes presumably reduced permeability, the steamflood process was effective in reducing oil saturation to zero in the steam-contacted portion of the reservoir.« less