Low-permeability Sandstone Gas Reservoirs Research Articles

Optimization of wellbore multiphase pipe flow calculation model for low permeability sandstone gas reservoir in Ordos Basin

The study of wellbore vertical pipe flow is the basis of reasonable production allocation and wellbore size optimization. According to the characteristics of low water gas ratio in sandstone gas reservoir of a gas field in Ordos Basin, the bottom hole pressure of typical gas wells in this area is calculated by using various wellbore pipe flow models such as Hagedorn brown, beggs Brill, Mukherjee Brill, gray and Aziz; Based on the measured bottom hole pressure, the relative performance coefficient evaluation method is used to optimize the wellbore calculation method. The results show that for the sandstone gas reservoir with low water gas ratio in gas field a, the calculation results of Hagedorn Brown model are in good agreement with the test results, so it is appropriate to use the Hagedorn Brown model to calculate the vertical pipe flow characteristics.

Study of the Seepage Mechanism in Thick Heterogeneous Gas Reservoirs

The seepage mechanism plays a crucial role in low-permeability gas reservoirs. Compared with conventional gas reservoirs, low-permeability sandstone gas reservoirs are characterized by low porosity, low permeability, strong heterogeneity, and high water saturation. Moreover, their percolation mechanisms are more complex. The present work describes a series of experiments conducted considering low-permeability sandstone cores under pressure-depletion conditions (from the Xihu Depression in the East China Sea Basin). It is shown that the threshold pressure gradient of a low-permeability gas reservoir in thick layers is positively correlated with water saturation and negatively correlated with permeability and porosity. The reservoir stress sensitivity is related to permeability and rock composition. Stress sensitivity is generally low when permeability is high or in the early stage of gas reservoir development. It is also shown that in sand conglomerates, especially the more sparsely filled parts, the interstitial materials among the conglomerates can be rapidly dislodged from the skeleton particles under stress. This material can therefore disperse, migrate, and block the pore throat producing serious, stress-sensitive damage.

Natural Fractures in Low-Permeability Sandstone Reservoirs in the LD-A HPHT Gas Field, Yinggehai Basin: Implications for Hydrocarbon Exploration and Development

Research on the characteristics and distribution of natural fractures is of great importance for the exploration and development of low-permeability sandstone gas reservoirs. In this study, fracture identification and characterization were carried out using cores and imaging logging. Then, comprehensive fracture development indicators were constructed to predict the distribution of fractures in wells by conventional logging. The main factors that affect the development of natural fractures and the implications of fractures on hydrocarbon exploration and development were discussed. The results showed that the natural fractures were mainly low-angle tectonic fractures in sandstone reservoirs. Most of fractures are unfilled, but the distribution of the fractures in the thin sections has a discrete fracture structure, indicating that the connectivity of the fracture system is poor. The development of natural fractures is mainly influenced by rock strength, petrographic composition, and petrology, and the fractures are more developed in sandstones with a higher content of brittle minerals. The fracture densities are mainly distributed below 0.05 m/m and up to 0.1 m/m. In the present in situ stress state, all of the natural fractures in the LD-A gas field are invalid fractures. The critical pressure of the natural fracture is approximately 16.5–25.4 MP/km; when the pore pressure exceeds this value, the fractures become effective fractures. These results provide new geological knowledge and guidance for the exploration and development of LD-A gas fields and other low-permeability tight sandstone reservoirs.

Natural gas development prospect in Changqing gas province of the Ordos Basin

At present, natural gas accounts for a low proportion in China's primary energy consumption structure and is highly dependent on foreign sources. Changqing gas province of the Ordos Basin where PetroChina Changqing Oilfield Company (referred to as Changqing Oilfield) is located is one of China's four major natural gas production bases. It bears the important responsibility for ensuring people's livelihood and promoting the healthy development of society economy. In recent years, Changqing Oilfield actively implements national instructive spirit on vigorously promoting domestic oil and gas exploration and development strength and formulates the secondary acceleration development strategies. Its annual natural gas production in 2020 reaches 448.5 × 108 m3 and oil and gas equivalent exceeds 6000 × 104 t, tamping its important position of “Western Daqing” in this industry. In order to further promote the continuous stable production and realize the goal of quality and efficiency improvement in Changqing gas province, this paper analyzes the situations and challenges of natural gas development in this gas province, prepares the development technological countermeasures and forecast the natural gas development prospect. And the following research results are obtained. First, the natural gas exploration and development in Changqing gas province is divided into four stages and the main technologies for the development of low-permeability carbonate gas reservoir, low-permeability sandstone gas reservoir and tight sandstone gas reservoir are formed. Second, the natural gas development in Changqing gas province faces six challenges, such as low reserve production degree, sharp decline of production rates and complex distribution of remaining undeveloped reserves of developed gas fields. And twenty-six development technological countermeasures are put forward correspondingly, such as well pattern thickening, extension and reserve increase, secondary production layer potential tapping and fine gas well management. Third, the development direction and goal of natural gas development in Changqing gas province is to pay equal attention to the stable production of old gas fields and the production increase of new areas and carry out conventional gas and unconventional gas research simultaneously. In conclusion, the annual natural gas production of Changqing gas province will maintain a sound momentum of steady growth and will exceed 500 × 108 m3 at the end of the 14th Five-Year Plan and maintain at a stable level for a long term, which is conducive to the optimization of domestic energy consumption structure and realization of “carbon peak and carbon neutrality”.

Numerical Simulation of the Non-Darcy Flow Based on Random Fractal Micronetwork Model for Low Permeability Sandstone Gas Reservoirs

Darcy’s law is not suit for describing high velocity flow in the near wellbore region of gas reservoirs. The non-Darcy coefficient β of the Forchheimer’s equation is a main parameter for the evaluation of seepage capacity in gas reservoirs. The paper presented a new method to calculate β by performing gas and con-water flow simulations with random 3D micropore network model. Firstly, a network model is established by random fractal method. Secondly, based on the network simulation method of non-Darcy flow in the literature of Thauvin and Mohanty, a modified model is developed to describe gas non-Darcy flow with irreducible water in the porous medium. The model was verified by our experimental measurements. Then, we investigated the influence of different factors on the non-Darcy coefficient, including micropore structure (pore radius and fractal dimension), irreducible water saturation ( S wi ), tortuosity, and other reservoir characteristics. The simulation results showed that the value of the non-Darcy coefficient decreases with the increase in all: the average pore radius, fractal dimension, irreducible water saturation, and tortuosity. The non-Darcy coefficients obtained by the fractal method of microparameters are estimated more precisely than the conventional methods. The method provides theoretical support for the productivity prediction of non-Darcy flow in gas reservoirs.

Low-Salinity-Assisted Cationic Polyacrylamide Water Shutoff in Low-Permeability Sandstone Gas Reservoirs

The application of polymer-based relative permeability modifiers (RPM) in low-permeability sandstone reservoirs has long intrigued production engineers. We hypothesize that lowering salinity may ex...

Natural Gas Reservoir Characteristics and Non-Darcy Flow in Low-Permeability Sandstone Reservoir of Sulige Gas Field, Ordos Basin

In order to reveal the gas–water distribution and formation mechanism of the low-permeability sandstone gas reservoir, the gas reservoir distribution and the formation mechanism in a low-permeability sandstone gas reservoir are investigated using data obtained from a physical simulation experiment of gas percolation. The exploration and experimenting for petroleum in the upper Paleozoic gas pool of the Sulige gas field in the Ordos basin in this paper. Results showed that the gas reservoir is characterized by low gas saturation, a complex distribution relationship of gas–water, and weak gas–water gravity differentiation. The characteristics of gas distribution are closely related to permeability, gas flow, and migration force. The capillary pressure difference is the main driving force of gas accumulation. There exists a threshold pressure gradient as gas flows in low-permeability sandstone. The lower that permeability, the greater the threshold pressure gradient. When the driving force cannot overcome the threshold pressure (minimal resistance), the main means of gas migration is diffusion; when the driving force is between minimal and maximal resistance, gas migrates with non-Darcy flow; when the driving force is greater than maximal resistance, gas migrates with Darcy flow. The complex gas migration way leads to complicated gas- water distribution relationship. With the same driving force, gas saturation increases with the improvement of permeability, thus when permeability is greater than 0.15 × 10−3 µ m2, gas saturation could be greater than 50%.

Research on Potential Evaluation of Gas Well Refracturing and Fuzzy Comprehensive Well Selection Method

The gas reservoir in the B area is low-permeability sandstone gas reservoir, with complex geological conditions, low permeability and strong heterogeneity and often needed refracturing. While the number of gas wells in the B district was large, leading to difficulty in well selection, and the mining effect of refracturing was affected by many factors, thus it is difficult to conduct quantitative research using conventional methods.Based on the field data in the B area, the potential and fuzzy comprehensive well selection software for gas well refracturing is developed. The paper established the developed potential system of gas reservoir in the B area, calculated recoverable reserves using a type water drive curve, and analyzed potential area by drawing the monthly gas production contour curve,which provided a guiding basis for the decision of refracturing well selection. The fuzzy comprehensive evaluation method was applied to analyze the main factors affecting the refracturing well selection, and the fuzzy comprehensive evaluation model was established to optimize many wells in the B district.Practice results show that the well selection technology based on the combination of the potential area evaluation system and the fuzzy comprehensive evaluation method is reliable, and the refracturing well preferred has obtained good results.

Influence of Bound and Mobile Water on Gas Well Production in a Low-Permeability Sandstone Gas Reservoir

The influence of mobile and bound water on seepage capability of a low-permeability sandstone gas reservoir was studied and formulas were derived to calculate gas well production rate using cores from Xujiahe low-permeability sandstone gas reservoir in China. It is shown that mobile water in the well exerts a stronger negative effect on gas production than bound water. If the pressure gradient is too steep, a small part of the bound water may turn into mobile water, whereupon the gas seepage efficiency falls. So, use of controlled pressure is recommended for gas production, which in the end enhances the gas recovery efficiency of the reservoir.

Physical Properties and Main Controlling Factors of Low-Permeability Sandstone Gas Reservoir

In order to guide the resource prediction and exploration evaluation of low-permeability sandstone gas reservoir, the physical properties of this kind of gas reservoir are summarized from such aspects as lithology, porosity, permeability and the characteristics of capillary force, and the main controlling factors of the gas reservoir are analyzed. The analysis show that low-permeability sandstone gas reservoir is mainly characteristic of high capillary pressure, high bound water saturation, low and high porosity as well as low permeability. Rock composition and structural characteristics of the reservoir is the basis of the factors that can affect the compactness of the reservoir. The formation of the reservoir is mainly affected by deposition, diagenesis and late tectogenesis: deposition can affect the composition of minerals, the original physical properties of clastic sediments and others; diagenesis is the main stages of the densification of reservoir, where compaction, pressure solution, cementation and late dissolution are the causes of the densification of reservoir. Dissolution and rim chlorite cementation improve reservoir property; tectonization can have an effect of late transformation on the physical properties of clastic reservoir. At the same time, the fluid characteristics in the reservoir can also affect the permeability of reservoirs.

Nuclear Magnetic Resonance Measurements of Original Water Saturation and Mobile Water Saturation in Low Permeability Sandstone Gas

We use nuclear magnetic resonance (NMR) and centrifugation to measure the original water saturation and mobile water saturation of cores from the Xujiahe low permeability sandstone gas reservoir, and compare the NMR results with the corresponding field data. It is shown that the NMR water saturation after 300 psi centrifugation effectively represents the original water saturation measured by weighing fresh cores. There is a good correlation between mobile water saturation and the water production performance of the corresponding gas wells. The critical mobile water saturation whether reservoir produces water of the Xujiahe low permeability sandstone gas is 6%. The higher the mobile water saturation, the greater the water production rate of gas well. This indicates that well's water production performance can be forecasted by mobile water saturation of cores.

Fracture Swarms in Low-Permeability-Sandstone Gas Reservoir Rocks in New Mexico, Colorado, and Wyoming: Implications for Exploration and Development

Fracture permeability is of primary importance to producibility of gas from many low-permeability sandstone gas reservoirs in the western US; but the location, orientation, spacing, and connectedness of fractures in the subsurface are difficult to measure directly. Maps of fractures provide the most accurate representation of fracture spatial distribution, trace length, connectivity, and size and shape of fracture-bounded blocks. In this study, fracture patterns were characterized by mapping five large exposures of Pictured Cliffs and Frontier sandstone along the margins of the San Juan and Green River basins. A set of fractures, interpreted as having formed in flat rocks prior to local Tertiary folding and uplift, is recognized in both formations. In contrast to the conventional model of regional fractures in which fractures are arranged in regularly spaced, orthogonal arrays, these fractures occur in discrete swarms separated laterally by domains that either lack fractures or have only rare fractures. These less fractured domains may be as much as several hundred meters wide. Within swarms, fractures are well interconnected along the length of the swarm but poorly interconnected across the width of the swarm. Fractures between swarms are commonly isolated. For the Pictured Cliffs and Frontier outcrops that were studied, themore » fracture pattern is self-similar over scales ranging from outcrop to interwell scale with fractal dimension D {approximately}1.2. In low-permeability sandstones of the Rocky Mountain region, irregularly spaced fracture swarms are potential targets for gas exploration and should be incorporated into fractured-reservoir models.« less

Significance of Natural and Coring-Induced Fractures in Travis Peak Formation for Reservoir Stimulation: ABSTRACT

ABSTRACT Efficient hydraulic facture treatment of low-permeability sandstone gas reservoirs depends on an assessment of natural-fracture length, width, and abundance and on reliable predictions of the stimulation-fracture strike, which generally is parallel to the maximum horizontal stress. Analysis of 565 natural and coring-induced fractures in more than 1,800 ft of whole core from seven wells in the Lower Cretaceous Travis Peak Formation in East Texas (Fig. 1), together with borehole televiewer and other fracture-imaging logs from three wells, shows that (1) the abundance, physical properties, and orientation of natural fractures could potentially affect the success of hydraulic fracture treatment and (2) the orientation of coring-induced petal and petal-centerline fractures can be used to infer the direction of stimulation-fracture propagation. Reservoir sandstone in the Travis Peak contains subvertical natural extension fractures that are locally open in the subsurface with widths of as much as 0.2 in (5 mm) (Fig. 2) at depths of greater than 9,900 ft in hydrostatically pressured rocks. Fractures are more abundant in the hinges of gentle monoclines and in sandstone with pervasive quartz cement. Natural fractures strike east-northeast (Fig. 3), but they are not precisely parallel to the direction of stimulation-fracture propagation. During hydraulic fracture treatment, these characteristics will tend to cause fracture branching, curvature, and development of auxiliary fractures. The resulting tortuous fracture network, variable fracture widths, and potential for leakoff of treatment fluid could promote screenout and, consecquently, inefficient fracture treatment, if not considered in fracture treatment design. Figure 1. Structural setting of the study area (outlined by box) in the northern Gulf of Mexico basin. FIGURE 2. [Grey Scale] Natural extension fracture in Travis Peak Formation sandstone at 9842 ft (3000 m), S.A. Holditch & Associates SFE No. 2, Nacogdoches County, TX. Long dimension of the photograph is 4.7 in (12 cm). Figure 3. Rose diagram of natural extension-fracture attitudes in the Travis Peak Formation, East Texas. End_of_Record - Last_Page 591-------