An unequal fracturing stage spacing optimization model for hydraulic fracturing that considers cementing interface integrity

Determining reasonable fracturing stage spacing is the key to horizontal well fracturing.Different from traditional stage spacing optimization methods based on the principle of maximum stimulated reservoir volume,in this paper,by considering the integrity of the wellbore interface,a fracture propagation model was established based on displacement discontinuity method and the competition mechanism of multifracture joint expansion,leading to the proposal of an unequal stage spacing optimization model.The results show that in the first stage,the interfacial fractures spread symmetrically along the axis of the central point during that stage,while in the second and subsequent stages,the interfacial fractures of each cluster extend asymmetrically along the left and right sides.There are two kinds of interface connectivity behaviour:in one,the existing fractures first extend and connect within the stage,and in the other,the fractures first extend in the direction close to the previous stage,with the specific behaviour depending on the combined effect of stress shadow and flow competition during hydraulic fracture expansion.The stage spacing is positively correlated with the number of fractures and Young’s modulus of the cement and formation and is negatively correlated with the cluster spacing and horizontal principal stress difference.The sensitivity is the strongest when the Young’s modulus of the cement sheath is 10-20 GPa,and the sensitivity of the horizontal principal stress difference is the weakest.

Synchronous injection-production energy replenishment for a horizontal well in an ultra-low permeability sandstone reservoir: A case study of Changqing oilfield in Ordos Basin, NW China

It is difficult to build an effective water flooding displacement pressure system in the middle section of a horizontal well in an ultra-low permeability sandstone reservoir.To solve this problem,this study proposes to use packers,sealing cannula and other tools in the same horizontal well to inject water in some fractures and produce oil from other fractures.This new energy supplement method forms a segmental synchronous injection-production system in a horizontal well.The method can reduce the distance between the injection end and the production end,and quickly establish an effective displacement system.Changing the displacement between wells to displacement between horizontal well sections,and point water flooding to linear uniform water flooding,the method can enhance water sweeping volume and shorten waterflooding response period.The research shows that:(1)In the synchronous injection and production of horizontal well in an ultra-low-permeability sandstone reservoir,the water injection section should select the section where the natural fractures and artificial fractures are in the same direction or the section with no natural fractures,and the space between two sections should be 60?80 m.(2)In addition to controlling injection pressure,periodic water injection can be taken to reduce the risk of re-opening and growth of natural fractures or formation fracture caused by the gradual increase of water injection pressure with water injection going on.(3)Field tests have verified that this method can effectively improve the output of single well and achieve good economic benefits,so it can be widely used in the development of ultra-low permeability sandstone reservoirs.

Development of fractures in soft rock surrounding a roadway and their control

As the excavation of roadway, new fractures will be formed and the pre-existing fractures extend with the redistribution of stress in surrounding rocks. Eventually, fracture zone and bed separation are formed in rocks because of the developed fractures. Therefore, mastering the fracture evolution of surrounding rocks is very important to maintain the stability of roadway. The surrounding rocks of main haulage road- way in a certain coal mine is so broken and loose that the supporting is very difficult. Based on compre- hensive anal[ysis of the engineering geological conditions, a sight instrument was used to observe the fractures of internal surrounding rocks, Four indices, i.e., the width of fracture zone W, the number of fractures n, the width of fractures d and rock fracture designation RFD, are put forward to evaluate the fracture dewelopment. According to the evolution rules of the soft rock roadway from this paper, control principles by stages and by regions are presented through the research. At the same time, the best time of grouting reinforcement is determined on the basis of fracture saturation. Field practice shows that the roadway can satisfy normal production during service periods by suitable first support and grouting reinforcement.

Optimization of acid fracturing for a tight carbonate reservoir

In this study,acid fracturing treatments were simulated for a tight limestone reservoir within a shale formation using FRACPRO software.The purpose was to investigate the optimum acid fracturing design that leads to a higher fracture etched length and width,and higher fracture conductivity.Moreover,the impact of the rock-acid contact time and whether to consider a post-flush or fluids flowback,on the acid fracturing outcomes were also investigated.A simple geological model was constructed which consists of different lithological layers.Different acid fracturing design scenarios were considered starting from a single stage of acid injection to multi-stage treatment.In multi-stage acid treatment,alternate acid-slickwater injection was considered.Plain HCl acids with different concentrations and other acids that are already included in FRACPRO database were used.The results showed that the acid loss during post-flush is among the main problems of the acid fracturing in tight carbonate shale reservoir.For the single stage of acid injection,it is recommended to flow back the acid after well shut-in instead of considering a post-flush stage.The multi-stage alternate acid slickwater injection reduces or even eliminated the acid loss.However,it is recommended to inject a slickwater before well shut-in to reduce the rock-acid contact time,thus reducing the formation damage.The results also showed that the created fracture etched width decreases and the fracture etched length increases as the fracturing stages increase.In this study,because of the low carbonate layer permeability and compressive strength,a two-stage alternate 28%HCl and slickwater injection with a post-flush stage is recommended.

Reservoir forming conditions and key exploration and development technologies for marine shale gas fields in Fuling area, South China

Although shale gas resources are abundant in China,commercial discoveries have not been made before the discovery of Fuling Shale Gas Field.SINOPEC has done lots of theoretical and technological studies on marine shale gas development in China.Research shows shale gas has dynamic accumulations with early preservation and late reconstruction and proposes high-quality shale developed in deep-water shelf as the base and good preservation conditions as the key factor for shale gas accumulation.Key technologies and facilities were developed for geophysical survey of shale gas,design and optimization of shale gas development,drilling and completion of horizontal wells,and fracturing stimulation.As the first and largest shale gas field in China,the discovery and successful development of Fuling Shale Gas Filed has made China the first country to achieve large-scale development of shale gas after North America.By August 2017,Fuling Shale Gas Field had declared 6008.14×10^(8)m^(3) proven reserves,76.8×10^(8)m^(3) production capacity and 133.9×10^(8)m^(3) cumulative production.The construction of Fuling Shale Gas Field with high level,high speed and high quality has been a good example of shale gas development in China.Its successful experiences can be used to other fields and play an important role in optimizing energy structure and improving environment.