Since 2007, an operator in Nigeria has registered a significant increase of oil-spill events caused by sabotage and oil-theft activities. The risks for personnel safety and environmental protection were such that it was decided to investigate new detection and monitoring systems. The technology presented here allows detecting and locating leaks taking place at a distance from the sensor of up to 35 km. The technology of this system is based upon discrete vibroacoustic sensing. This technology takes advantage of the fact that any acoustic signal reaching, or generated upon, the pipeline will introduce vibroacoustic waves within the pipeline body and the transported-fluid medium (crude oil, brine, and natural gas).
The industry spends significant amount of time and money to optimize completion designs to develop various unconventional resource plays, including cluster spacing or fracture spacing. It is strongly believed that better reservoir characterization and better modeling technique selection ought to shorten the learning curve and save money. This article reviews the state-of-the-art on fracture spacing optimization and discusses the challenges that the industry is facing to achieve an optimal cluster spacing decision. The current technology to develop unconventional resource plays is a horizontal well with multistage hydraulic fracturing treatments. Since permeability is extremely low ( 0.001 md) in unconventional resource reservoirs, multiple fractures are needed to have economic well rates, as shown in the image on top (Figure 1).
Explanations for how fracturing works are often based more on the imaginations of experts than observations of the damage caused by hydraulic pressure. A rare study that spent the tens of millions of dollars required to get a direct look at horizontal wells drilled in South Texas (URTEC 2670034) described its findings as "very different from the simple view of the stimulated reservoir volume commonly modeled or predicted with current fracture models." The paper added: "The absence of proppant on most of the hydraulic fractures indicates that proppant emplacement is quite different from idealized transport model predictions." And, "The apparent side-by-side propagation of closely spaced, near parallel hydraulic fractures also differs from the output of currently accepted fracture models and may call into question the role of stress shadowing in hydraulic fracture propagation." When the paper was delivered at the Unconventional Resources Technology Conference (URTEC) last August, it generated a lot of buzz among experts starved for direct observations.
Zhang, Ruxin (State Key Laboratory of Petroleum Resources and Engineering China University of Petroleum-Beijing) | Hou, Bing (State Key Laboratory of Petroleum Resources and Engineering China University of Petroleum-Beijing) | Shan, Qinglin (State Key Laboratory of Petroleum Resources and Engineering China University of Petroleum-Beijing) | Lin, Botao (State Key Laboratory of Petroleum Resources and Engineering China University of Petroleum-Beijing) | Lu, Yunhu (State Key Laboratory of Petroleum Resources and Engineering China University of Petroleum-Beijing) | Wang, Yajun (PetroChina Changqing Oilfield Company) | Zhang, Xiang (PetroChina Changqing Oilfield Company)
Coplanar perforation is a new perforation technology with unique perforation position that can improve the efficiency of hydraulic fracturing of horizontal wells in low permeability reservoirs which have low porosity, low permeability and are difficult to explore. So it is important to know how fractures initiate and propagate as well as the optimal perforation parameters.
A large-scale true tri-axial hydraulic fracturing simulation experiment is conducted to study fracture initiation characteristic and propagation pattern of coplanar perforation in horizontal wells under different in-situ stresses, compared with conventional helix perforation in horizontal wells under the same in-situ stresses. In the meantime, the three-dimensional finite element method is used to study the influences of different perforation parameter combinations set according to field data on fracturing pressure in horizontal wells, including shot length, shot diameter and shot density.
The experiment results show that the coplanar perforation has simpler fracture propagation pattern under higher stress difference and has following advantages compared to conventional helix perforation: (1) reducing the fracturing pressure, (2) controlling the fracture propagation to reduce the complexity of near-wellbore fracture and (3) reducing the near-wellbore friction resistance. The numerical simulation results show that: (1) the fracturing pressure does not decrease linearly as the shot density increases, it falls rapidly when the shot density increases from 9 to 15 holes per meter, but when the shot density increases from 15 to 21 holes per meter, it falls slowly and finally remains almost constant, (2) the fracturing pressure decreases as the shot diameter increases, and (3) the fracturing pressure stays the same as the shot length increases. Through the conclusions of experimental and numerical simulation, we could provide some valuable suggestions to the hydraulic fracturing on filed. During hydraulic fracturing process in low permeability reservoirs, coplanar perforation technology with high shot density (21 holes/m) and large shot diameter (0.03m) should be used.
The experimental and numerical simulation conducted in this paper show a real process of hydraulic fracturing with coplanar perforation. The advantages and optimal perforation parameters of coplanar perforation are proposed to give guidances for hydraulic fracturing on field.