Third EAGE International Science and Applications workshop Far East Hydrocarbons 2014

During the work comparative analysis of geological models on North Veninsky field was perform. Was defined how can verify the geological model and volume and possible reserves of hydrocarbons depending on quantity of needed information. Shows the necessity for further exploration on the field based on the results of additional research on the example of the acoustic data inversion and subsequent modeling litho-petrophysical characteristics. Analysis of the all data and considered various options of exploration well design was made by author. Performed calculation of the cost-effectiveness of further exploration of the oilfield depending on the chosen well construction variant.

Geosphere tool. From initial concept through execution and post-drill analysis the ENL Geoscience team and Schlumberger’s Well Placement Group worked closely to define and deliver the well’s objectives. During the execution phase real time decisions were being made at every stand down. Schlumberger’s well placement team was co-located at the ENL office for the duration of the zone 18 reservoir penetration, working 12 hour shifts with overlapping support. Likewise ENL geoscientists and contract operations geologists worked parallel 12 hour shifts to ensure real-time decision making was smooth and efficient.

Dynamic simulation of the geological (static) model for Sakhalin Energy’s Piltun and Astokh fields indicates that the model does not capture the subsurface accurate enough to allow acceptable history matching of actual production data. Since this means that the predictability of the models is low as well (which complicates proper field development) it was decided to re-build the model and replace the existing layer-based model with a facies-based one. The 3D seismic data for the Piltun-Astokhskoye field was re-processed as well since the previous model and the improved imaging was used to update the seismic interpretation based on Sequence Stratigraphic principles.

Piltun forms the northernmost part of the larger Piltun-Astokhoye oil, gas and condensate field, located in shallow offshore waters off the north-eastern shores of Sakhalin Island. The development targets multiple stacked oil rim accumulations within an asymmetrical anticlinal structure. The primary reservoirs are shallow marine clastic deposits of the Upper Miocene Lower Nutovsky Formation. Whilst the original Piltun-Astokh appraisal campaigns addressed the first-order field uncertainties by defining the stratigraphy, structure, reservoir distribution and quality, fluid fill and short term well in-flow performance, significant second-order uncertainties remained unresolved. Information on mid- to longer term reservoir performance was generally lacking as the development concept for the field was defined. This required planning for the acquisition of such data early on in the implementation phase. This paper explains how Well and Reservoir Surveillance data was acquired, interpreted and used to drive business decisions in the Initial, Interim and Current phases of the development.

Following a period of almost a decade, a commercial version of the Towed Streamer EM System was tested over a number of producing fields in the Norwegian and British sectors of the North Sea in October 2012. One of the most challenging tests was over the Alvheim Boa field located 2,100 m below the seafloor. The results demonstrate the system can be used effectively for reservoir detection and delineation. A new processing technique to enhance the sensitivity of CSEM data to a resistive reservoir anomaly is especially suited to the towed streamer EM system. Known as optimised Synthetic Aperture (SA) processing, when applied to the data acquired at the Alvheim Boa field, it resulted in significantly improved signal strength.

Mud log gas acquisition techniques remained fairly constant for a long period. Modern gas acquisition techniques have improved from technical innovation, resulting in truly digital mud log gas data. Modern rig design has evolved at a greater pace than mud log gas acquisition techniques. The type of gas data acquisition equipment chosen is now more important to assure quality data is obtained. Wells examined that were expected to have similar gas readings actually had highly variable measurements. Investigation showed this variation was due to mud levels changing dramatically over short periods of time. There is a direct relation between gas acquisition equipment and rig circulation system design. A review should be done of the planned rig design and efficiencies prior to determining the gas acquisition system to be used on the rig. If a modern gas acquisition system is chosen for the first time in an area, added efforts to recalibrate these data to traditional gas acquisition should be considered to assure results.

The article covers possible changes to Unified Stratigraphic Chart of Paleogene-Neogene deposits of Sakhalin. Such changes are based on paleontological and lithological data obtained as a result of study of 34 well logs on the shelf of the Okhotsk sea and Tatar Strait. Regional unconformities were identified that divide sedimentary cover into seismic sequences corresponding to stratigraphic horizons. Seismic-stratigraphic chart of Cenozoic deposits was built.

Based on new seismic data acquired by Dalmorneftegeophysica JSC in 2010-2012 (Seismic Survey DRS CDP 108*, Gravity Survey, Magnetic Survey), an alternate interregional correlation scheme of basic unconformities was proposed and the age of sedimentary cover in the Chukchi, Easter-Siberian and Laptev Seas was proved. The delivered results give evidence of Late- Palaeozoic-Cenozoic age of the North Chukchi basin and Aptian-Cenozoic age of the Laptev Sea and Novosibirsk basins.

We demonstrate the success of combining wavelet shift tomography, full waveform inversion (FWI) and separated wavefield imaging (SWIM) for pre-stack depth migration (PSDM) velocity model building and imaging. The workflow is referred to as Complete Wavefield Imaging (CWI) as it utilizes reflection, multiple, and refraction arrivals in the dual-sensor seismic data. Wavelet shift tomography, operating on reflection arrivals, was used to update the shallow overburden in a legacy PSDM velocity model. FWI updates based on matching modelled versus observed refraction arrivals were subsequently able to resolve high resolution velocity variations associated with channels, pockmarks and gas pockets in the shallow overburden. Additionally, gathers from SWIM were generated using up- and down-going separated wavefields uniquely provided by the dual-sensor data. The SWIM approach exploits the greater illumination of the near surface inherent in the multiple arrivals. SWIM image gathers were used to validate the longer wavelength features not seen by FWI. The study illustrates how reflection, refraction, and multiple arrivals from dual-sensor data can contribute towards high-fidelity model building and imaging. Resolution of the complex shallow overburden leads to more accurate positioning and depth predictions for the reservoir, directly impacting estimation of reserves.