Xu, Yandong (Research Instittue of Petroluem Engineering, Sinopec North-West Branch) | Pang, Wei (State Key Laboratory of Shale Oil and Gas Enrichment Mechanisms and Effective Development, Sinopec Research Instittue of Petroluem Engineering) | Li, Shuanggui (Research Instittue of Petroluem Engineering, Sinopec North-West Branch) | Zou, Ning (Research Instittue of Petroluem Engineering, Sinopec North-West Branch) | Du, Juan (State Key Laboratory of Shale Oil and Gas Enrichment Mechanisms and Effective Development, Sinopec Research Instittue of Petroluem Engineering) | Mao, Jun (State Key Laboratory of Shale Oil and Gas Enrichment Mechanisms and Effective Development, Sinopec Research Instittue of Petroluem Engineering)
Shunnan Block in North-West China is one of the toughest HPHT gas reservoirs with vertical depth over 7500 m, formation temperature over 200 and pressure gradient varying from 1.3 to nearly 2. The condition is close to temperature and pressure limit of well testing tools, therefore, the tools are hard to be sent to downhole and chances are that well testing operations usually failed. The pressure buildup data are with bad quality and needed to be converted into downhole data. Meanwhile, it's hard to diagnose accurate flow regimes and interprete because the block is typically carbonate reservoirs with porous medium including pores, natural fractures and caves.
In this paper, we reviewed the exploration wells in this block and find that interpretation by pressure buildup or transient production data can only reflect part of the formation information; therefore the two kinds of data are combined to get more accurate interpretation results. For pressure buildup interpretation, three models including dual porosity model, composite model, and dual porosity with composite model are chosen and compared. For the production data, dual porosity model with boundary is selected because the wells usually show characteristics of multiple porous medium and boundary dominated flow. Parameters interpreted from pressure buildup data are simultaneously transferred into the model for production data.
Results show that the combined interpretation by pressure buildup and production data can reduce the un-uniqueness of models as well as enhancing the accuracy of formation and wellbore parameters evaluation. The model and parameters can satisfy both pressure buildup and production data history. Although Shunnan block is considered as one greatly promising reservoir from the short period open flowing, the combined interpretations suggest very limited drainage volume. Reasons for this paradox phenomenon may be that the wells are severe contaminated by drilling fluid, or the wells were only producing gas in caves and natural fractures nearby the wells while other caves are not connected.
Kirchhoff Time Migration (KTM) is a traditional seismic imaging technique used by geophysicists, a numerical method related to the Greens function solution of the scalar wave equation. KTM has been used routinely in some form or another for at least forty years, and a variety of computational implementations exist within academic and industrial settings. The KTM algorithm is relatively simple, however the high dimensionality of the overall data processing problem makes computation fairly expensive and thus a good candidate for High Performance Computing (HPC). In recent years, the Graphical Processing Unit (GPU) has taken a significant place among HPC platforms used for computationally intensive tasks such as seismic imaging. This work outlines a novel strategy for implementing the KTM algorithm in CUDA, which demonstrates excellent scaling and timing properties as compared to a CPU implementation.
Computational cost and storage requirement are the main obstacles that inhibit the research and practical application of full waveform inversion (FWI). We have developed a fast parallel scheme to speed up FWI on graphics processing unit (GPU),which is a parallel computing device, via CUDA(an acronym for Compute Unified Device Architecture), developed by NVIDA and used as the programming environment. In this parallel scheme, to avoid frequent and low-bandwidth data transfer between host memory and device memory, almost the entire computing task, including propagator and backpropagator, are coded as a sequence of kernel functions that can be called from the compute host for each iterative inversion. The random boundaries conditions are used when propagating source wavefield to solve the storage requirement so that we do not have to save any additional wavefield data and the noise introduced into final inversion image is so weak that can be ignored due to iterations. To test our algorithm, we implement the FWI on Personal Computer (PC) with GTX480 GPU to reconstruct the Marmousi velocity model using synthetic data generated by the finite-difference time domain code. This numerical test indicates that the GPU-based FWI typically is 80 times faster than the CPU-based implementation.
Stewart, Robert R. (University of Houston) | Dyaur, Nikolay (University of Houston) | Omoboya, Bode (University of Houston) | de Figueiredo, J.J.S. (Unicamp-Brazil) | Willis, Mark (ConocoPhillips) | Sil, Samik (ConocoPhillips)
Physical modeling, using ultrasonic sources and receivers over scaled exploration structures, plays a useful role in wave propagation and elastic property investigations. This paper explores the anisotropic response of novel fractured glass blocks created with a laser-etching technique. We compare transmitted and reflected signals for P- and S-waves from fractured and unfractured zones in a suite of ultrasonic experiments. The unaltered glass velocities are 5801 m/s and 3448 m/s for P and S waves, respectively, with fractured zones showing a small decrease (about 1%). Signals propagating through the fractured zone have decreased amplitudes and increased coda signatures. Reflection surveys (zero-offset and variable polarization and offset gathers) record significant scatter from the fractured zones. The glass specimens with laser-etched fractures display a rich anisotropic response.
We present a new gravity gradient inversion method for estimating a 3D density-contrast distribution defined on a grid of prisms. Our method consists of an iterative algorithm that does not require the solution of a large equation system. Instead, the solution grows systematically around user-specified prismatic elements called “seeds”. Each seed can be assigned a different density contrast, allowing the interpretation of multiple bodies with different density contrasts and that produce interfering gravitational effects. The compactness of the solution around the seeds is imposed by means of a regularizing function. The solution grows by the accretion of neighboring prisms of the current solution. The prisms for the accretion are chosen by systematically searching the set of current neighboring prisms. Therefore, this approach allows that the columns of the Jacobian matrix be calculated on demand, which greatly reduces the demand of computer memory and processing time. Tests on synthetic data and on real data collected over an iron ore province of Quadrila´tero Ferri´fero, southeastern Brazil, confirmed the ability of our method in detecting sharp and compact bodies.
Uwaga, Anthony (Centrica Energy) | Yan, Jun (Centrica Energy) | Jackson, Peter (Centrica Energy) | Onafeko, Samson (Centrica Energy) | Lukins, Paul (Centrica Energy) | Farrow, Chris (Integrated Production Technologies)
The York gas field is located in the Southern North Sea (SNS) area of the United Kingdom Continental Shelf (UKCS).
Structurally the field is interpreted as having a good number of intra-faults. Of particular interest to this paper is the intra-fault located south-west of the field. Due to the presence of this fault there are two separate crests in the southern area of the field. Each of these two crests was targeted by a horizontal well in the initial development plan of the field. A third horizontal well was to be drilled and completed in the eastern flank of the field.
Recent subsurface studies involving petrophysical, geological and reservoir engineering re-interpretation and analysis carried out in the field confirmed the well count, but not the well type, required for development of the field as compared to previous development plan. Furthermore, it was established that by drilling and completing across the aforementioned south-western intra-fault, instead of avoiding it as done in the previous development plan, the total well count for developing the field is reduced by one.
Two optimal development scenarios, both having similar recoveries, have been identified for the development of the field. Option 1 has two development wells and requires drilling and completing across an intra-fault. Option 2 requires three development wells and no across fault drilling/completion. Economic analysis of the two development options shows that option 1 has better economics indices. Thus, though option 1 is deemed challenging because it requires drilling/completing across a fault the cost savings to be realised from implementing a two well development, instead of the three wells required in option 2, makes it more attractive, nevertheless.
The paper presents the basis and merits of adopting option 1 as the preferred development option for the field. It further discusses the challenges and issues associated with drilling/completing across a fault and way-forward plans to be adopted for a successful implementation of the option 1 development plan.
The paper concludes by presenting option 2 as a contingency option to be implemented in the event that option 1 is not successful with regards to drilling/completing across the aforementioned intra-fault.
Zhang, Xiaoqin (Daqing Oilfield Co. Ltd.) | Pan, Feng (Daqing Oilfield Co. Ltd.) | Guan, Wenting (Daqing Oilfield Co. Ltd.) | Li, Dan (Daqing Oilfield Co. Ltd.) | Li, Xia (Daqing Oilfield Co. Ltd.) | Guo, Songlin (Daqing Oilfield Co. Ltd.)
The molecular weight of polymer is important to the efficiency of polymer flooding. Polymer solutions with higher molecular weight have better absorption, better capitation, higher resistance and residual resistance coefficients. All these imply higher recovery factor. But for reserviors of middle and low permeability, higher injected molecular weight means more unswept pore volume, lower controlling degree and recovery factor. Therefore, both higher injected molecular weight and controlling degree must be fully considered, so as to obtain a higher recovery factor in a given block.
On the basis of lab experiments and numerical simulations, two matching charts are formed. One is about the relationship between molecular weight and layers and the other is about controlling degree on recovery rate. They are used to optimize the molecular weight for polymer flooding. This new method is applied in the project for polymer flooding in secondary layers of Daqing oilfield and an enhanced recovery factor of more than 8% is obtained.
In polymer flooding, the solution viscosity is enhanced and water phase permeability is reduced. Sweeping volume is enlarged to increase recovery factor. Polymer molecular weight is the main factor in polymer flooding. Higher molecular weight means lower water phase permeability and higher recovery rate. However, in the industrialization of polymer flooding in Daqing Oilfield, it is indicated molecular weight should be optimized in accordance with permeability. Ultrahigh molecular weight needs high injection pressure and causes blocks in the layers, which leads to poor development. To the question, a new method is put forward to optimize the molecular weight.
EMEPMI and PETRONAS have recently concluded major simulation studies on the application of immiscible Water Alternating Gas (WAG) injection to enhance oil recovery for Tapis and Guntong fields, the two largest waterflooded fields operated by ExxonMobil in Malaysia. Both fields have been under waterflood operation for more than 25 years with about 40% original-oil-in-place (OOIP) recovered to-date.
Evaluations of immiscible WAG injection process application at Tapis and Guntong fields were carried out using full-field reservoir simulation models. The scope of the evaluation work included: a) assessment of additional recovery from enhancing waterflood operations, b) assessment of recovery uplift from WAG injection, c) WAG pattern and WAG ratio optimization, d) optimal WAG operating parameters and reservoir management strategy, and e) integrating production and injection well operating conditions with facilities process design.
The Tapis WAG evaluation study has supported ExxonMobil's plans to implement a WAG project at Tapis. The study has matured to the point of providing the subsurface design basis for the Project. The Guntong study has provided an initial assessment of WAG potential used for the conceptual WAG development and
early project planning.
Malaysia‘s oil predominantly comes from offshore fields. Malay Basin located to the East of Peninsular Malaysia contains most of the country's oil reserves. In the maturing oil fields of Malaysia, EOR options are being field-tested for enhancing and prolonging production. A Water Alternating Gas (WAG) pilot was implemented in the Dulang Field S3 Block during 2002-6. The S3 Block contained six wells (three producers and three injection wells) in two reservoirs namely E12/13 and
This pilot project was the first EOR pilot in Malaysia. The main objectives of the pilot project were to design and develop the EOR scheme, and to evaluate the feasibility of WAG injection to maximize the oil recovery from this and other similar oil fields. A comprehensive monitoring was undertaken to assist in evaluation of pilot performance. Identification of optimal operating conditions, Dulang field-specific screening criteria and success indicators were perceived to be germane
for future WAG implementation.
Oil bearing sands of the Dulang field were deposited under fluvial or near shore environments as parts of sand-shale sequences. These strata were subsequently folded and faulted, resulting in discrete `compartments` with uncertain flow continuity across various faults. Due to existence of numerous major as well as, minor faults and thinness of shale layers at certain places, the critical considerations for EOR were a) confinement of the injected fluids within individual compartments,
and b) flow continuity between different injector and producer wells. It was therefore decided to use different water and gas phase tracers at each of the three injection wells within the S3 block. The data gathered were used for assessing internal communication, flow parameters and inter-well reservoir heterogeneity such as high permeability streaks. This paper discusses details of the tracer program and significant responses observed during the pilot implementation.
Daqing oilfield is a heterogeneous sandrock oilfield with multilayers. The application of polymer flooding in the field has obtained significantly technological and economic effects. On the bases of numerous lab experiments, it is indicated that polymer solutions of high concentration and molecular weight have better absorption and captation toward the layers than normal solutions do. Besides, the resistance and residual resistance coefficients are much larger. The higher the concentration and molecular weight are, the larger the increment in viscoelasticity is. Once polymer flooding with high concentration and molecular weight is applied, the residual oil saturation will decrease and displacing efficiency will increase. All these lead to higher increment in recovery rate.
Three pilot tests were conducted by means of high concentration and molecular weight. On the bases of the obtained results, industrialized application of the recovery method first began in the N1 block of Sazhong Area in Daqing oilfield in Jan. 2009. In that block, the molecular weight of the polymer solution was 25million Dalton and the concentration was 2000mg/L. Maximum decrement in water cut was 30 percent and enhanced recovery rate was 8.3 %. It was estimated that enhanced recovery rate could ultimately reach 18 percent by the end. The successful application of polymer flooding with high concentration and molecular weight in Daqing oilfield would provide practical experience for the development of similar reservoirs.