Changqing Oilfield Research Articles

Exploration and practice of integrated control technology for tubing and sucker rod lopsided wearing in directional well

Changqing oil field generally used sucker rod pump. In 2015, the maintenance operations reached 42 thousand times, the cost is about 550 million RMB, the work caused by tubing and sucker rod lopsided wearing accounts for 42.8% of the total. This paper focused on the main factor of lopsided wearing which caused high frequency of maintenance work, a three-dimensional mechanical simulation model of sucker rod string was established based on the analysis of borehole trajectory, rod mechanics; A model for calculation the neutral point of double material composite pipe and steel tubing is carried out; The calculation method of allowable stress is modified; at the same time, the application conditions of the mature process is standardized, to achieve the integration of technology management. The sucker rod lateral force dynamic distribution and allowable stress calculation method, the sucker rod parameter optimization and real-time warning, optimization of structure and the amount of wear resistant pipe string have been applied in oilfield. Compared with 2015, The number of maintenance operations decreased more than 6000 wells, operation frequency by 0.99 times / year - wells decreased to 0.85 times / year - wells, which is composed of 14 thousand and 500 well tube and rod failure wells decreased to 13 thousand and 300 wells, decreased 8%, annual cost savings of nearly 60 million RMB. It will have important guiding significance to prolong the pump checking period and cost control.

Investigation on the transient pressure response of water injector coupling the dynamic flow behaviors in the wellbore, waterflood-induced fracture and reservoir: Semi-analytical modeling and a field case

Abstract There is growing evidence showing that water injection may induce formation fracturing around injectors in tight reservoirs. Because waterflood-induced fractures (WIFs) are not strengthed by proppants, they close gradually during the field-testing period, which results in “fracture-closure-induced” flow rate, shrinking fracture length (SFL) and decreasing fracture conductivity (DFC). In this paper, we propose a novel semi-analytical model to characterize the bottom-hole pressure (BHP) behavior of water injectors by coupling the dynamic flow in the wellbore, WIF, and reservoir. Flows between reservoir and WIF are linked through a fracture-storage coefficient and fracture-face skin factor, while flows between WIF and wellbore are coupled via wellbore-storage coefficient and choked-fracture skin factor. Perturbation theory method is deployed to include the DFC effect, and Duhamel principle is invoked to characterize flow rate changes caused by wellbore and fracture storage effects. Results show that bi-storage effects can be identified as two unit slopes in the pressure derivative curve. In the absence of extra pressure drop between wellbore and WIF, i.e., choked-fracture skin equals to zero, a prolonged storage period with a considerably large storage coefficient can be obtained. In addition, we find that SFL could cause the variable fracture storage effect while DFC may lead to the upward of pressure derivative curve at late times. Finally, the model is successfully applied in the Changqing Oilfield to validate its reliability.

A Comprehensive Work Flow To Characterize Waterflood-Induced Fractures by Integrating Real-Time Monitoring, Formation Test, and Dynamic Production Analysis Applied to Changqing Oil Field, China

Summary It is well-known that water injection may induce formation fracturing in tight reservoirs. Especially when the field-geology condition is complex and the waterflood-induced fractures (WIFs) are not well-identified in time, the induced fractures can be of the same order as the well spacing, which has a significant, and generally undesired, impact on both areal sweep and vertical conformance. Therefore, the onset of WIFs must be identified in a timely manner, and the waterflooding performance must be evaluated comprehensively to formulate an appropriate strategy over time. A new work flow, containing analytical/semianalytical, statistical, and numerical techniques that are based on flow-rate/BHP and formation-testing data, is applied to identify the WIFs, diagnose waterflooding direction and front distribution, analyze interwell connectivity, and interpret abnormal bottomhole-pressure (BHP) behaviors in the Changqing Oil field. The work flow includes three modules: First, real-time monitoring and analysis, including modified Hall plot, evolving skin analysis, and injection/fracturing index methods, are used to identify the start of WIFs. Then, the formation-testing module, consisting of step-rate test (SRT), radioactive-tracer logging, and passive seismic method, is applied to investigate the formation-fracturing pressure, and uneven waterflooding performance in the areal and vertical directions. On the basis of the two former modules, we adapt the third module, which includes injector/producer relationships (IPRs) and the constrained multiple-linear-regression (MLR) method, to quantitatively investigate the waterflooding direction by injection/production rates. A new model—injection well with waterflood-induced fracture (IWWIF)—is proposed to characterize the abnormal BHP behaviors considering the properties variation (shrinking fracture length and decreasing fracture conductivity) of WIFs during the falloff period. Compared with an individual method, the ITD (which is the abbreviation of WIF identification, formation testing, and dynamic production analysis) work flow is developed to obtain a comprehensive and deep understanding of waterflooding performance. The main emphasis of this study is to integrate different approaches to address the key uncertainties rather than analyze each data source individually. On the basis of the results obtained by this work flow, the operators can make a more-proactive and -reasonable decision on waterflooding management. The work flow proposed in this paper gives a useful guidance in short- and long-term waterflooding management in tight reservoirs.

Pressure-transient analysis of water injectors considering the multiple closures of waterflood-induced fractures in tight reservoirs: Case studies in Changqing Oilfield, China

Abstract There is growing evidence showing that water injection may induce formation fracturing, and the injection well may experience multiple fracture closures during fracture falloff period. Such dynamic behavior of waterflood-induced fractures (WIFs) needs to be carefully assessed and controlled through a waterflooding program. The objective of this study is to develop a pressure transient analysis procedure to analyze the bottom-hole pressure (BHP) responses of water injection wells with the consideration of the dynamic behavior of WIFs. We propose a rigorous physical process that integrates mini-fractures initiation, communication, propagation and closure throughout waterflooding. The piecewise function is used to characterize the consecutive closure of fractures during the shut-in period. Based on the proposed model, the pressure-transient solutions are obtained and the type curves are plotted. Results indicate that the consecutive fractures closure lowers the rate of pressure drop and results in the fluctuations of the pressure derivative curve. During the field-testing period, the water that stored in the WIFs would be squeezed into the matrix since there are no proppants inside, which behaves similar with wellbore storage effect. Meanwhile, due to the different stress conditions in the fracture walls, they close successively after shutting in the well, which results in the multiple storage effect that characterized by several unit slopes in the pressure derivative curve. Finally, several cases studies from Changqing Oilfield have validated the practicability of the models to evaluate the BHP performances of water injectors.

Isolation and characterization of biosurfactant-producing and diesel oil degrading Pseudomonas sp. CQ2 from Changqing oil field, China.

In the present research investigation, 13 indigenous bacteria (from CQ1 to CQ13) were isolated from soil collected from Changqing oil field of Xi'an, China. Four promising biosurfactant producers (CQ1, CQ2, CQ4, and CQ13) were selected through primary screening among these 13 strains, including via drop collapse and oil-spreading methods. However, only the strain CQ2 showed the best biosurfactant production and was further screened by hemolytic assay, cetyl trimethyl ammonium bromide (CTAB), surface tension and emulsifying activity. The bacterium CQ2 has the ability to produce about 3.015 g L−1 of biosurfactant using glucose as the sole carbon source without any optimization. The produced biosurfactant could greatly reduce surface tension from 72.66 to 24.72 mN m−1 with a critical micelle concentration (CMC) of 30 mg L−1 and emulsify diesel oil up to 60.1%. The cell-free broth was found to be stable in wide temperature (4–100 °C), pH (6–12) and salinity (2–20%) ranges for surface and emulsifying activity. This biosurfactant was preliminarily found to be of a glycolipid nature as evident from thin-layer chromatographic (TLC) and Fourier transform infra-red spectroscopic (FTIR) analyses. Moreover, CQ2 was able to degrade 54.7% of diesel oil, which surprisingly could form a substantial amount of bioflocculants during the degradation process. Furthermore, the 16S rDNA sequence using the Genbank BLAST tool revealed that isolated CQ2 was closely related to species of Pseudomonas genus and, thus, was entitled Pseudomonas sp. CQ2. The results of residual diesel oil contents measured by GC-MS showed that C7–C28 hydrocarbons could be degraded by Pseudomonas sp. CQ2. Thus, these findings revealed that CQ2 could be applied for remediation of diesel oil/petroleum-contaminated waters and soils on a large scale.

长庆油田油套损伤检查技术对比及应用

长庆油田油套损伤检查技术对比及应用

Co-optimization of oil recovery and CO2 storage for cyclic CO2 flooding in ultralow permeability reservoirs

Cyclic CO2 flooding is an efficient method to enhance oil recovery in ultralow permeability reservoirs. As the demand for low carbon economy development, co-optimization of CO2 storage and utilization should be considered. In this research, initially a comprehensive optimization method was proposed, which co-optimize oil recovery and CO2 storage by different weighting factors. Then, a series of core flooding experiments were performed using the core samples collected from Changqing oilfield, which is a ultralow permeability reservoir with heterogeneity and micro-cracks, CO2 injection parameters of slug size and Injection-Soaking Time Ratio (ISR) were optimized. The results revealed that the optimal injection parameters changed for different optimization objectives. In the case where equal important to oil recovery and CO2 storage were considered, the optimum CO2 injection parameters in the ultralow permeability reservoirs were 0.03PV for slug size and 1:1 for ISR. Comparing the method of oil recovery optimization (ω 1 = 1) to co-optimization of oil recovery and CO2 storage (ω 1 = ω 2 = 0.5), oil recovery was reduced by 8.93%, CO2 storage was significantly increased by 25.85%. The results provide an insight into parameter optimization of CO2 enhanced oil recovery design.

Preparation and application of a novel phenolic resin dispersed particle gel for in-depth profile control in low permeability reservoirs

Abstract Phenolic resin dispersed particle gel (PDPG) was successfully prepared from bulk gel by a mechanical shearing method. The effects of bulk gel strength, shearing time, shearing rate, and bulk gel-water ratio on the PDPG particles were systematically analyzed. The morphological results showed that the PDPG particles have a round shape with nano-size to micron-size distribution. The shearing rate is one of the most critical factors in the preparation, while the shearing time and bulk gel strength are secondary factors in preparing the PDPG particles. In addition, the bulk gel-water mixing ratio has a slight impact on the prepared PDPG particles. The PDPG particles had a good shearing resistance and expansion capacity which enhances their application performance in oilfields. Sand pack flowing experiments indicated that PDPG particles can easily enter the in-depth formations and effectively plug high permeability channels. The higher the formation permeability ratio of sand packs, the better the profile improvement rate. By retention or adsorption in large permeability zones, trapping and bridging across pore throats or large channels, the prepared PDPG particles can effectively improve the formation profile and divert the following water into low permeability zones, and then the oil is enhanced. The injection of PDPG particles was first successfully applied to Changqing Oilfield in China which provided a reference to control water production in other similar low permeability mature oilfields.

Semi-analytical modeling for water injection well in tight reservoir considering the variation of waterflood - Induced fracture properties – Case studies in Changqing Oilfield, China

It is well acknowledged that water injection may induce formation fracturing in tight reservoir, and the injection well may experience shrinking fracture length (SFL) and variable fracture conductivity (VFC) during fracture-falloff period, which shows the bi-storage behavior. However, available pressure-transient analysis (PTA) models hardly consider these effects (SFL, VFC and bi-storage behavior) on pressure-transient response, which can lead to erroneous results. This paper aims at presenting an innovative approach to model the water injection wells considering the dynamic characteristics of waterflood-induced fracture (WIF). We first modeled fluid flow between reservoir and the fracture which characterized by fracture-storage coefficient and fracture-face skin factor, and flow between wellbore and the fracture which represented by wellbore-storage coefficient and choked-fracture skin factor. In addition, the effects of SFL and VFC were included by finite difference method. A semi-analytical solution was then derived to model injection well with waterflood-induced fracture (IWWIF). Finally, this methodology has been successfully applied in Changqing oilfield, China. There are six flow regimes for the IWWIF model in the tight reservoir, including wellbore-storage regime, transitional-flow regime, fracture-storage regime, the second transitional regime, linear flow regime and bilinear flow regime. Compared to current models, the bi-storage phenomenon is discovered and validated as two straight lines with unit slope in the pressure derivate curve of type plot. The WIF that closely links with the wellbore can be regarded as an “expanding wellbore”, which illustrates the reason that the “wellbore-storage coefficients” are increased by up to several orders of magnitude in a great many of water injection wells. The VFC behavior could cause the upward of pressure-derivative curve, which is generally recognized as the characteristic of closed boundary condition while the variable fracture-storage effect may occur because of SFL. In addition, the relation between matched fracture-storage coefficient and fracture length is given, which provides us another way to obtain the probable length of WIF. Finally, this new model has been successfully used to evaluate well performance and reservoir characteristics based on bottom-hole pressure (BHP) history of five field cases in Changqing oilfield, China.

Unexpected viscoelastic deformation of tight sandstone: Insights and predictions from the fractional Maxwell model

Tight gas is one important unconventional hydrocarbon resource that is stored in tight sandstone, whose mechanical property greatly influences the tight gas production process and is commonly believed to be simply elastic when designing the stimulation plan. However, the experimental evidence provided in this work surprisingly shows that tight sandstone can deform in a viscoelastic way. Such an unexpected observation poses a challenge in accurately modelling the deformation process. We solve this problem by adopting the fractional Maxwell model to successfully derive the constitutive equation of tight sandstone, based on which not only all the experimental data can be interpreted quantitatively, but also reasonable and consistent predictions as to tight sandstone’s long-term deformation behaviour can be made. We then investigate the typicality of our results in China’s Changqing oilfield, which is one major centre of tight gas production and where the rock samples for experiments are obtained. It is estimated that a non-negligible portion of 18% tight sandstone samples in this area will probably display viscoelasticity. Finally, our work implies that the mechanical properties of other materials may also need further scrutiny to possibly uncover any unexpected behaviour, overlooking which may result in misleading predictions.

Predicting Waterflooding Performance in Low-Permeability Reservoirs With Linear Dynamical Systems

Summary Several interwell connectivity models such as multiple linear regression (MLR) and the capacitance model (CM) have been proposed to model waterflooding performance in high-permeability reservoirs on the basis of observed production data. However, the existing methods are not effective at characterizing the behavior of transient flows that are prevalent in low-permeability reservoirs. This paper presents a novel dynamic waterflooding model that is based on linear dynamical systems (LDSs) to characterize the injection/production relationships in an oil field during both stationary and nonstationary production phases. We leverage a state-space model (SSM), in which the changing rates of control volumes between injector/producer pairs in the reservoir of interest serve as time-varying hidden states, depending on the reservoir condition. Thus, the model can better characterize the transient dynamics in low-permeability reservoirs. We propose a self-learning procedure for the model to train its parameters as well as the evolution of the hidden states only on the basis of past observations of injection and production rates. We tested the LDS method in comparison with the state-of-the-art CM method in a wide range of synthetic reservoir models including both high-permeability and low-permeability reservoirs, as well as various dynamic scenarios involving varying bottomhole pressure (BHP) of producers, injector shut-ins, and reservoirs of larger scales. We also tested LDS on the real production data collected from Changqing oil field containing low-permeability formations. Testing results demonstrate that an LDS significantly outperforms CM in terms of modeling and predicting waterflooding performance in low-permeability reservoirs and various dynamic scenarios.

Production Analysis of Tight Sandstone Reservoir in Consideration of Stress-Sensitive Permeability

Background: Tight sandstone reservoirs play an important role in the oil industry. The permeability of tight sandstone reservoir generally has stronger stress sensitivity than that of conventional reservoir because of the latter’s poor physical properties. However, the production analysis of tight sandstone reservoir did not fully considered the stress-sensitive permeability yet. Objective: This paper proposed a production analysis method considering the stress- sensitive permeability. Method: This paper firtstly investigated the stress sensitivity characteristics and the effect of stress-sensitive permeability on a tight reservoir. Decline-type curves that consider stress-sensitive permeability are then established, and a systematic analysis method was built for the production analysis to obtain the single-well controlled dynamic reserves and reservoir physical properties. Results: A field analysis was performed in combination with Block Yuan-284 of Changqing Oilfield. Results show that with the reduction of reservoir pressure, stress sensitivity leads to the decline in reservoir permeability and the increase in seepage resistance, thus reducing the actual single-well controlled reserve and radius. Conclusion: By utilizing the analysis method based on the decline curves, we can effectively predict the single-well controlled dynamic reserves of such reservoirs and evaluate the characteristic parameters of reservoirs.

Complete genome sequence of a versatile hydrocarbon degrader, Pseudomonas aeruginosa DN1 isolated from petroleum-contaminated soil

Pseudomonas aeruginosa DN1 was isolated from a petroleum-contaminated soil from Changqing Oilfield with its capability to degrade high molecular weight polycyclic aromatic hydrocarbons (HMW PAHs) and crude oil. Herein, the whole genome sequence analysis of P. aeruginosa strain DN1 was reported, consisting of a size of 6,641,902 bp chromosome assembled genome (67.09 mol% G + C content) and a 317,349 bp plasmid assembled genome (57.01 mol% G + C content). According to the genome information, strain DN1 encodes various genes related to degradation of aliphatic hydrocarbons and aromatic compounds. In addition, DN1 contains gene clusters for biosynthesis and regulation of biosurfactant rhamnolipids. These genes may serve as a basis of further elucidation of the genetic background of this promising strain, and provide insights into investigating the metabolic and regulatory mechanisms of hydrocarbon biodegradation. • The whole genome sequence of P. aeruginosa strain DN1 was consisted of a size of 6,641,902 bp chromosome assembled genome. • The chromosome genome harbors various genes related to degradation of aliphatic hydrocarbons and aromatic compounds. • Gene clusters for biosynthesis and regulation of biosurfactant rhamnolipids are included in the chromosome genome.

Complete Genome Sequence of Enterobacter sp. Strain ODB01, a Bacterium That Degrades Crude Oil.

ABSTRACTEnterobacter sp. strain ODB01, which was isolated from the Changqing oil field, can degrade crude oil efficiently and use crude oil as its sole source of carbon and energy. We report the complete genome sequence of ODB01. The results promote its application in the remediation of petroleum contaminants.

Exploitation Evaluation of Tight Oil Reservoirs in Yanchang Formation Using Horizontal Well: A Case Study of Some Wells from Changqing Oilfield, Ordos Basin

Horizontal wells development technology has become an important means to improve the production of a single well. In this paper, according to the reservoir characteristics of tight oil of Yanchang Formation, some optimizations of horizontal well technology were made and applied in some wells. Through evaluating the exploitation effect concluding yield evaluation, regression and water content evaluation and single well evaluation of these wells, it can be seen that the single well production is enhanced greatly.

Natural gas exploration and development in Changqing Oilfield and its prospect in the 13th Five-Year Plan

Abstract PetroChina Changqing Oilfield Company (hereinafter referred to as Changqing Oilfield) built the largest oil and gas production base of China in the Ordos Basin in 2013, achieving the yearly natural gas production of 375 × 10 8 m 3 in 2015. For the further sustainable and stable production and quality and benefit improvement, such great achievements made in the 12th Five-Year Plan were first summarized, and the relevant favorable conditions for natural gas development were also analyzed as follows: abundant natural gas resources; increasingly mature EP continuously improved delicacy management; and a surging demand for natural gas. Then, challenges to natural gas development were also discussed, including obvious deterioration of natural gas resources; diminished capacity of stable production of produced gasfields; increasing number of low-yield wells; and prominent supply–demand contradiction in present natural gas market. Finally, its prospect in the 13th Five-Year Plan was studied: to carry out natural gas exploration with focus on Upper Paleozoic tight gas, Lower Paleozoic carbonate rocks, and new areas and new domains, so as to achieve rapid growth of natural gas reserves and orderly replacement in exploration domains; to make rational development planning with focus on the stable production of mature gasfields; and to enhance tight gas recovery and strengthen capacity building in new areas, so as to achieve a steady rise of annual gas production in the giant gas province. It is expected that by the end of 13th Five-Year Plan period, Changqing Oilfield will achieve its annual gas production of up to 400 × 10 8 m 3 .

Waterflood Direction and Front Characterization With Four-Step Work Flow: A Case Study in Changqing Oil Field China

Summary Because of the effect of reservoir heterogeneity and fractures in low-permeability reservoirs, effective characterization of waterflood direction and front has become a challenging issue under high-water-cut condition. To achieve better understanding of such a complex problem, a work flow, containing statistical and numerical techniques, is developed to characterize waterflood direction and front distribution in Changqing oilfield by using both flow rates and bottomhole-pressure (BHP) data. The work flow includes four steps: First, dynamic analysis is used to qualitatively investigate the relationships between injector and producers; then, the constraint multiple-linear-regressions (MLR) method is applied to calculate the interwell-connectivity coefficients, which was used to quantitatively describe the waterflood direction by production and injection rates. On the basis of the results of the two former steps, we can adopt numerical well testing as our third step to deal with flow rates and BHP data to characterize the waterflood direction and front. Finally, the streamline method is used to simulate the waterflood front and high-permeability-channel distribution on the basis of the outcome of the three preceding techniques. Compared with individual methods, the proposed work flow can offer more perspectives and ways to make a comprehensive and deep investigation of the waterflood reservoir. The results obtained by this work flow enable proactive and better waterflood management in the Well Group W16 in Changqing oil field; namely, the water cut of producers decreases, meanwhile the oil production increases by nearly 40% referring to the field data in 2015. With the help of the information obtained by this work flow, operators could make more-reasonable decisions on waterflood management such as well-pattern optimization and injection–production parameters adjustment.

Characteristics and resource prospects of tight oil in Ordos Basin, China

Abstract Efficient large-scale development of ultra-low-permeability reservoirs (0.3–1 mD) has been achieved in the Changqing Oilfield, Ordos Basin of China. According to unique features of petroleum exploration and development in this basin, tight oil herein refers to petroleum that occurs in oil-bearing shales and interbedded tight sandstone reservoirs adjacent to source rocks with ambient air permeability 1×109 t of oil resources in shale in the 7th member of the Yanchang Formation and approximately 0.9×109 t and 1.1×109 t of tight sandstone oil resource in the 6th and 7th members of the Yanchang Formation, respectively. These tight oil resources are the realistic resources addition for the oilfield, which can ensure an annual production of 50×106 t of oil and gas equivalent and maintain long-term stable oil production in the Changqing Oilfield, Ordos Basin, China.

Analysis on innovation of geological exploration technology in petroleum development process

In recent years, with the booming of petroleum industry and the continual reserve urgency of fossil oil, petroleum exploration technology in China is required to be a higher level. At present, with the improvement and development of computing technology and other technology, China's fossil oil exploration technology have been greatly improved, the oil field work has a stage improvement, petroleum exploration technology has also improved, Shaanxi Changqing Oilfield has also made remarkable progress, and it is worth mentioning that the three main techniques, the exploration technology of well logging technology, drilling technology and exploration technology, have made great progress on innovation through using new technologies. But it does not mean that the petroleum exploration technology has met the requirements of petroleum development. Petroleum exploration technology is insufficient and needs to be unremittingly combined with other techniques for its improvement and innovation. Based on this, this paper studies and analyzes the innovation of geological exploration technology in petroleum development process

Water Plugging and Acidizing Combination Technology on Fractured Water Breakthrough Oil Well in Low Permeability Reservoirs

During the exploration in low permeability reservoirs, oil wells are usually abruptly flooded because of the connection between injection wells and oil wells through fractures and large pore canals, causing the productivity decrease in the integral block. In this research a combination plugging agent consisting of weak gel, strong gel and temporary plugging agent is used to plug fractures and large pore canals and improve formation homogeneity by multi-slug injecting. The basic performances of gel plugging agent and the solubility of the temporary plugging agent in different solvents were determined. Furthermore, the selective plugging ability of combination plugging agent and the feasibility of the new technology were evaluated. The results show that combination plugging agent can reduce the permeability of high permeability core more than 99%, while hardly reduce the low permeability core, and by subsequent acidizing treatment, the permeability of low permeability core was increased more than 30 times, while high permeability core have be increased only a litter. Field application has been conducted in Changqing oil field. All of the three pilot tested wells are getting a good improvement. After the application of the combination technology, oil production is increased by 2.7 t per day of each well. And water content is reduced by 42.9% on average. The effective time is more than 418 days. This technology has increased 3,260.4 tons of oil and obtained an obvious effect.