Lu, Mingjing (China University of Petroleum, Colorado School of Mines) | Su, Yuliang (China University of Petroleum) | Wang, Wendong (China University of Petroleum) | Zhang, Ge (Xianhe Oil producing Plant, Shengli Oilfield, Sinopec)
Refracturing treatment are performed since stimulation effect won't last for entire life. Screening wells for refracturing needs a systematic analysis of huge amounts of data. With literature review, it is obviously that there are many factors controlling the success of refracturing and factors may vary in different oilfields. Proper factors and data processing are the primary principle in candidate selection. The Integrated Multiple Parameters (IMP) method is presented to provide assists in selecting candidate wells.
After deeply researching over 200 restimulated wells, all factors thought to be related with success of refracturing are listed and analyzed, results show that single factor may have great influence on restimulation but no significant patterns can be obtained since too many factors making things complicated. The IMP method proposes five parameters which are all integrated by those single factors. It is emphasized that all parameters have physical or engineering meanings which makes it easier to quantify their correlation in refracturing. Besides, all the parameters are dimensionless which makes it easier for using in mathematical models and statistical analysis.
The five dimensionless parameters are developed considering the most important aspects of candidate wells selection which are showed as followed: fracture reorientation, well completion, reservoir depletion, production decline, oil-water well connectivity. Parameters are calculated for all the restimulated wells to dig into their correlation with the outcomes of refracturing. A simple decision model is built to help with screening wells for refracturing. Results shows that it is more executable to evaluate and predict the success of refracturing with these dimensionless parameters. Fracture reorientation parameter is the primary one to be considered since it leads to fracture reorientation which brings significant production increment. Then two types of potential wells are picked: (a) wells with dissatisfied initial well completion, low production decline rate and high oil-water connectivity parameter; (b) wells with satisfied initial well completion, high well completion parameter, low production decline parameter, reservoir depletion parameter and low oil-water connectivity parameter for wells that are not easy for fracture reorientation. Wells selected are proved to be refracturing potential which verify the reliability and accuracy of IMP method.
The IMP method is an improved approach integrating most of the important factors which makes candidate selection much more predictable and it succeeds in screening out more than 80% of the potential wells in field test. Also, it can be applied widely in different oilfields since all the parameters are dimensionless. By combining with some mathematical methods such as neural networks, it can even predict increment of the restimulation treatment.
The Kirchhoff Q PSDM technique is studied in this paper in order to compensate the amplitude and correct the distortion of phase due to seismic attenuation in the earth, during the seismic waves traveling through the earth, especially through the the gas cloud region, to improve the resolution of the imaging results, and to satisfy the requirements of industrial production. In order to improve the calculation efficiency of the QPSDM, a time domain interpolation strategy is also proposed. This strategy avoids the compensation in frequency doamin at each imaging point, which is time-consuming. The computation efficiency of Q migration has been greatly improved with our method, making the Kirchhoff QPSDM able to meet the needs of industrial production. By analyzing the sources of the high frequency noise, the time-variant gain-limits are used to suppress the high frequency noise in the compensation procedure. The numerical results show that the compensation method using the time-variant gain-limits can effectively compensate the energy of the severe attenuation region while suppressing the high-frequency noise. Finally, we test the QPSDM approach on synthetic data and field data. These examples demonstratethat the QPSDM approach could produce higer resolution images with imporoved amplitude and correct phase compared to the convetional PSDM. The Kirchhoff QPSDM technology realized in this paper has produced desirable seismic images while it is applied in many exploration areas such as Dagang, Daqing, Malaysia, Nanhai, etc.
Least-squares migration (LSM) has become an increasingly important imaging tool in the seismic industry. It can successfully address imaging issues related to insufficient illumination and mitigate both migration artifacts and noise. More recently, a number of case studies from around the world have shown that LSM provides greatly improved seismic imaging. However, only a few examples reveal its advantages in both imaging and amplitude-versus-offset (AVO) inversion. For the amplitude aspect, compensating the effect of anelastic absorption and elastic scattering during propagation inside the earth has become increasingly popular over the past few years. The anelastic absorption and elastic scattering causes frequency-dependent amplitude decay, phase distortion, and resolution reduction. This is often quantified by the quality factor commonly called Q model. This effect can be largely compensated through Q prestack depth migration (QPSDM). Therefore, QPSDM has become an effective solution for seismic imaging in areas where strong absorption anomalies exist in the overburden. However, the excessive noise often resulting from QPSDM poses a big challenge to its application. In this paper, we propose a least-squares Q migration (LSQM) method that combines the benefits of both LSM and QPSDM to improve the amplitude fidelity and image resolution of seismic data. We also demonstrate that both seismic imaging and AVO inversions at wells can be significantly enhanced through image-domain single-iteration least-squares QPSDM Kirchhoff migration.
D-X oilfield implemented an infill adjustment from 2013 to 2015, adding 101 development wells, two central processing platforms and two wellhead platforms. After the adjustment, the oil field greatly improved the engineering processing capacity, but it had also entered a period of rapid decline. In order to mitigate the decline and improve the recovery rate, 65 adjustment wells were implemented in this oilfield after the first adjustment. Based on the new drilling data and production data, earlier inefficient well management was turned a more efficient well management, where the engineering processing space is fully utilized, the decline of oil field is alleviated, and the development effect is greatly improved.
The anelasticity of subsurface medium will cause dissipation of seismic energy. It is challenging to derive an interval
Presentation Date: Tuesday, October 16, 2018
Start Time: 9:20:00 AM
Location: Poster Station 21
Presentation Type: Poster
Zhang, Yunlong (School of Geosciences and Technology, Southwest Petroleum University, China) | Yin, Cheng (School of Geosciences and Technology, Southwest Petroleum University, China) | Ding, Feng (School of Geosciences and Technology, Southwest Petroleum University, China)
In fluvial facies reservoirs, thin sandstone interbedding is very common. The thickness of these single sandstone layers is relatively thin, the lateral variation is complex. Because of the limits of seismic resolution and the influence of faults, identification of the sandstone boundaries is very difficult. In this paper, on the basis of previous study, we set up the model of a thin interbedded sandstone and analyze by forward modeling waveform changes in the seismic record, such as the strength, sharpness, stability, symmetry and continuity of the event. Subsequently, via the proposed method, waveform structure attributes were extracted from a period time window, which can identify the boundaries of thin interbedded sandstones. The validity of this technique was verified by the model and a practical application.
Presentation Date: Wednesday, October 17, 2018
Start Time: 1:50:00 PM
Location: 210A (Anaheim Convention Center)
Presentation Type: Oral
Tapping the remaining oil with horizontal wells is routinely used in high water-cut oilfields. However, it faces serious challenges in complex fluvial reservoirs with stacked sand body, horizontal interlayers, lateral barrier and complex water flooding conditions. Moreover, the depth uncertainty of the target interval, limited number of offset wells, rapid change of thickness, thin target intervals, and variable fluid contact have also increased the risks of the horizontal well placement. In order to locate the optimal positions of the horizontal wells, get the maximum recovery, reduce the risk of water flooding, minimize the drilling time, we propose a comprehensive well planning and optimization method based on multidisciplinary innovative techniques. New techniques from geology, geophysics, and drilling engineering are assembled to efficiently perform the challenging task.
Firstly, an improved interwell 3D correlation technique was proposed to characterize the single sand body. The technique can depict the vertical hierarcy of reservoir. Secondly, we propose a lateral boundary delineation technique based on seismic geometrical attribute. Combined with ant tracking algorithm, we are able to extract the 3D lateral discontinuous surfaces. Based on above technique, we can build detailed architecture model fast and optimize the positions of horizontal wells. Considering the geological uncertainty, the boundary mapping tool is used to optimize the well trajectories in real time to avoid the water flooded zone and shale zone, and to stay in the sweet zone.
We applied the integrated workflow in Q oilfield in Bohai Bay basin, East China. 112 horizontal wells are drilled. The drilling results proved that boundary mapping tool can achieve smooth landing of well path and delineate the accurate geometry and thickness variation of sand body which reduces the depth uncertainty of seismic horizon explanation, and keeps the horizontal well trajectories away from oil-water contact. The production results show that 86% horizontal wells have achieved low water-cut and high oil production rate. The total production rate of Q oil field has increased by 2.5 times.
In-situ upgrading process (IUP) is an attractive technology for developing unconventional extraheavy-oil reserves. Decisions are generally made on field-scale economics evaluated with dedicated commercial tools. However, it is difficult to conduct an automated IUP optimization process because of unavailable interface between the economic evaluator and commercial simulator/optimizer, and because IUP is such a highly complex process that full-field simulations are generally not feasible.
In this paper, we developed an efficient optimization work flow by addressing three technical challenges for field-scale IUP developments. The first challenge was deriving an upscaling factor modeled after analytical superposition formulation; proposing an effective method of scaling up simulation results and economic terms generated from a single-pattern IUP reservoir-simulation model to field scale; and validating this approach numerically. The second challenge was proposing a response-surface model (RSM) of field economics to analytically compute key field economical indicators, such as net present value (NPV), by use of only a few single-pattern economic terms together with the upscaling factor, and validating this approach with a commercial tool. The proposed RSM approach is more efficient, accurate, and convenient because it requires only 15–20 simulation cases as training data, compared with thousands of simulation runs required by conventional methods. The third challenge is developing a new optimization method with many attractive features: well-parallelized, highly efficient and robust, and with a much-wider spectrum of applications than gradient-based or derivative-free methods, applicable to problems without any derivative, with derivatives available for some variables, or with derivatives available for all variables.
This work flow allows us to perform automated field IUP optimizations by maximizing a full-field economics target while honoring all field-level facility constraints effectively. We have applied the work flow to optimize the IUP development of a carbonate heavy-oil asset. Our results show that the approach is robust and efficient, and leads to development options with a significantly improved field-scale NPV. This work flow can also be applied to other kinds of pattern-based field developments of shale gas and oil, and thermal processes such as steam-drive or steam-assisted gravity drainage.
The high costs associated with hydrocarbon exploration in deepwater have led to an increased business demand for acquisition and processing of high-resolution broadband seismic data. In this paper, we review our experience of working on the Shell Sandman 3D survey, which was acquired using variable-depth streamers and synchronized multi-level sources. We focus on the key factors that influence the surface seismic temporal resolution and the technologies that provide solutions to these challenges: (1) source deghosting using source designature with near-field hydrophone data; (2) receiver deghosting using the 3D deghosting algorithm; and (3) compensation for the Earth absorption using centroid frequency shift Q tomography (FS-QTOMO) and QPSDM. The extra-wide bandwidth obtained from these processes provides a final image with detailed resolution that enhances quantitative characterization, not only for shallow geo-hazards but also for resolving relatively thin reservoirs in the deep section. Therefore, we can conclude that broadband seismic methodologies coupled with advanced seismic processing techniques, provide an effective solution for generating high-resolution seismic images, especially in challenging areas.
Wang, Zongjun (CNOOC Research Institute) | Fan, Ting’en (CNOOC Research Institute) | Hu, Guangyi (CNOOC Research Institute) | Nie, Yan (CNOOC Research Institute) | Tian, Nan (CNOOC Research Institute) | Zhang, Xianwen (CNOOC Research Institute)
The quality factor is the parameter that characterizes seismic wave energy attenuation caused by underground medium. And it is a key parameter in the reservoir predication and hydrocarbon detection. Centroid frequency method is one of common methods to evaluate quality factor, which has high precision and stability. But this method needs the centroid frequency and bandwidth of spectrum, which mainly relies on the quality of seismic spectrum. Time-domain centroid frequency shift method (DCFS for short) directly estimates the quality factor according to calculating the centroid frequency and bandwidth of seismic wavelet in time domain. For constant-phase wavelet, its centroid frequency of spectrum is the instantaneous frequency of its envelope at the peak, and for Gauss window its bandwidth can be calculated by converting the envelope width (the product of them is constant).when seismic wavelet approximates to constant phase and Gauss window, we can calculate the centroid frequency and bandwidth in the time domain, then evaluate the quality factor according to the centroid formula, which avoids the extraction of seismic wavelet spectrum. The test of VSP down-wave model shows that the time-domain centroid frequency shift method is feasible and credible.