Well logging and testing are the focus of attention for SPD. Since the early development stages, SPD engineers established reservoir management and data acquisition and interpretation processes to allow efficient future field development and optimize oil recovery. A multi-disciplinary integrated team approach is used in combination with technology support from Shell’s technical expert groups to allow effective implementation of surveillance and reservoir management activities.
An extensive data-gathering programme had been implemented by SPD during the early drilling and production stage to collect essential static and dynamic data on reservoir description and well performance. This will assist in optimization of the drilling and completion campaign, well design, injection conversion timings and overall waterflood strategy. The well and reservoir surveillance programme was designed to mitigate major development risks that had been identified and to provide sufficient information for proper management of the field development. The surveillance programme is split into two main parts: the drilling/completion phase and production phase. The drilling and completion phase focuses on gathering fundamental geological, petrophysical and fluid data including fluid and core sampling, wire line logging and well testing. The production phase of surveillance includes production logging (flow, temperature, pressure and watercut profiles), well testing (build-ups, fall-offs, interference tests), repeated cased hole saturation logs and tracer injection.
Each production well in Salym fields has a standard set of logging operations applied to it, in particular density logs, gamma logs, spontaneous potential logs, calliper logs, neutron and acoustic logs, and modern modifications of array electrical logs. Over the years of the Salym project, SPD and contractor staff have considerably improved the efficiency of logging operations. Standard logs are now taken by a stack of logging tools in one trip (at the start of the project the operation required four trips), which has reduced the time required for a logging operation to 5 to 6 hours (the same operation took 16 hours at the start of the project). In April 2009, SPD completed a logging operation in 4 hours 40 minutes using a new ComboToll technology from one of its Russian contractors, Kogalymneftegeophysika (KNGF). This tool is similar to Western equipment, including the Platform Express (PEX) tool of Schlumberger, which is also used in Salym. The high accuracy of these tools gives a more accurate understanding of the thicknesses and properties of the pay interval.
Logging in wells with a significant outstep is done with the use of the TLC technology patented by Schlumberger. SlimAccess (Schlumberger) and ComboTool (KNGF) have been used, as well as stiff cable logging.
In each fifth well SPD and their contractors’ engineers conduct formation testing to measure formation pressure in various zones and layers of the reservoir and determine the mobility of the formation fluid. Each twentieth well has nuclear magnetic logs undertaken to study the porous and flow characteristics of the reservoir.
Among other high-end methods SPD applies in the Salym fields are electrical and acoustic microscanners to study the texture of rock and fractures, and dipolar shear sonic logs to study the unconformities in the lateral stress of the studied deposits. Surface and downhole microseismic surveys help evaluate the shape of fractures after a hydrofrac, and vertical seismic profiling helps combine seismic and logging data. SPD and contractor engineers use wireline formation testers and sidewall core samplers to recover samples of fluids and rock.
Coring is an important source of information about rock properties and oil saturation. Cores are extracted (with its initial saturation preserved) from approximately every twentieth production well and all new exploration wells in Salym fields. Core recovery from a well is now approaching 2000 m, with an average 98% of core recovered and preserved.
When the company started coring operations in 2004, the length of core recovered in one run ranged between 6 and 12 m. With time, and thanks to good cooperation with the coring contractor SibBurMash SPD improved the average length of one core run to 36 m, reducing the time required for a coring operation from 5-6 days to 2 days. In 2008, a record 48.5-meter 100% core run was extracted in West Salym, the longest rock sample recovered during the Salym development.
Excellent quality and near complete recovery of core provide the SPD petrophysical team with direct information on oil saturated intervals and oil to water contacts in various areas of the fields. When combined with logging data, it will provide extensive data to evaluate the whole range of properties of oil saturated intervals and, consequently, optimize production.
SPD is also doing a lot of studies to test residual oil saturation beyond the waterflood front. For this purpose, SPD recovered core with preserved saturation from one of the infill wells that cut through a water-flooded interval. The company is also testing special electrical and carbon-oxygen logs to measure oil saturation in a cased hole.
Production testing is gaining in importance for the successful development of the fields, measuring production and injection flow and the composition of produced fluids. These studies involve the use of Y-shaped bypass tools that allow logging tools to be run below an electric submersible pump (ESP) and conduct testing during normal production. This technology makes it possible to measure flow at any point in time without the need to pull out the downhole assembly.
SPD is one of the few oil companies that uses a Y-tool in a 7” casing. The completion with a Y-tool was first tested in Salym in July 2007. SPD engineers then successfully removed the plug to run a wireline logging tool in a well with a 50o inclination. The production logging tool was placed under the ESP to allow for the well logging operation irrespective of the status of the ESP. Since that time, 20 wells in the Salym group of field have been completed with this technology. This information on flows in various perforated intervals will be used to make plans to optimize production and improve the reservoir development process. Additionally, this solution also helps comply with the Technological Schema that requires that flow rates be recorded in all reference wells.
Creating clear and objective representation of the geological structure of a field requires both the capability to obtain quality input information and the ability to process it in a consistent and comprehensive manner. This also requires efficient management of multiple information flows, and the ability to properly manage and preserve data. In SPD logging information from a logging contractor is uploaded by the field geological service into a ‘field’ instance of the petrophysical software. At this stage field engineers make a preliminary estimate of the quality of acquired data and wellbore rock properties. The pre-processed data is then delivered to the head office of the company, where the staff of the central petrophysical service check (and, if required, correct) the results of the ‘field’ interpretation. That will be followed by a final conclusion on the properties of penetrated horizons, which will be used by technologists to work out perforation strategy and select appropriate electric submersible pump sizes.