Presentation on theme: "2015 - SPE Workshop in Arctic Norway March 11th – 12th 2015 | Harstad, Norway No flaring well testing (Injection Fall-off testing) Arild Fosså | Expro."— Presentation transcript:
SPE Workshop in Arctic Norway March 11th – 12th 2015 | Harstad, Norway No flaring well testing (Injection Fall-off testing) Arild Fosså | Expro Norway AS
SPE Workshop in Arctic Norway March 11th – 12th 2015 | Harstad, Norway Traditional well testing Low actual emissions, but aesthetically un-appealing Important data for development decisions Are there real alternatives ??
SPE Workshop in Arctic Norway March 11th – 12th 2015 | Harstad, Norway Background Dynamic Well Test data is used as input data for the following; Reservoir Model Well performance Model, and Pipeline and Facilities Models Key data provided are; Pressures, Temperatures Flow rates Fluid data (both PVT and large volume) Well Bore Pressure transient from a Well Test
SPE Workshop in Arctic Norway March 11th – 12th 2015 | Harstad, Norway Example of conseq. from missing data Business Development strategy Reservoir evaluation K Field knowledge Miss understand : heterogeneity org. K anisotropy Underestimate heterogeneity size Miss or not quantify extra permeability (fract., dissolution) Poor estimate : Reserves Production profiles Underestimate Production profiles Poor estimate segregation effects Overestimate : sweeping efficiency reserves Wrong decisions for recovery mechanism (gas/water injection, gas cycling/depletion) Overestimate Facilities Underestimate : Facilities Profitability Less Profits / Lose money Less Profits Project abandonment
SPE Workshop in Arctic Norway March 11th – 12th 2015 | Harstad, Norway Backdrop on the Barents Sea The big picture for the Barents Sea area is characterized as follows; – Same formal rules & reg’s as the rest of the NCS. – High focus from environmental groups – High focus on spill prevention from the authorities – High Political focus – (spills, blow-out risk, ice-edge, public opinion, etc. etc.) Due to this an alternative way of testing wells could be of interest.
SPE Workshop in Arctic Norway March 11th – 12th 2015 | Harstad, Norway What is needed for a Well Test? PorosityFrom cores ViscosityFrom Fluid Samples Flow ratesFrom Surface (normally) PressuresFrom Bottom Hole In addition it is important to minimize the accumulator effect downhole inside the string – Well Bore Storage effects. Due to this there is great freedom in how you achieve the above. The elaborate option……. Bideford Dolphin plant The “simple” option….. Gas test - Westhope, North Dakota, January 07
SPE Workshop in Arctic Norway March 11th – 12th 2015 | Harstad, Norway Injection Fall-off testing One of the parameters we have freedom over is the flow rate. Which is used to induce the pressure transient. There is nothing stopping us from doing an injection period rather than a flow period to get the pressure transient going. The equivalent to the normal pressure build-up would be a pressure Fall-off. Gives the same type of data as a normal well test. – Except Fluid Data - obtained during open hole logging. Classic Injection Fall-off test.
SPE Workshop in Arctic Norway March 11th – 12th 2015 | Harstad, Norway Injection Fall-off application Traditionally Injection Fall-off tests have been used for; – Water zones and water-flood projects. Measure pressure increases to accurately predict pressure rises from long-term fluid injection. – Verify that reservoir zones are «non-migration» types – i.e. no communication between reservoir zones. – Changes in permeability and skin over time. – Geothermal wells – Water disposal wells – Traditionally used for Gas Storage wells There isn’t anything stopping a wider use.
SPE Workshop in Arctic Norway March 11th – 12th 2015 | Harstad, Norway Injection Fall-off issues Issues associated with Injection Fall-off testing vs. normal Well Tests – First, the character of the system changes. Instead of single-phase flow, we are now faced with two-phase water/oil flow governed by relative permeability's – Second, injection of cold water induces temperature changes in the formation This complicates the pressure behaviour through temperature effects on the oil and water viscosities. – Third, injection of water may result in the formation accidentally fracturing and in coupling of rock mechanics and fluid flow problems. It is critically important for successful test interpretation to avoid accidental fracturing and to inject water at below the formation fracturing pressure.
SPE Workshop in Arctic Norway March 11th – 12th 2015 | Harstad, Norway Schematic saturation profile top view Mitigation #1 System character change Issue - Introduction of two-phase fluids in the reservoir affecting the relative permeability's Mitigation – Use theoretical «two- bank» and «multi-bank» models. – handles the two-phase aspect of an Injection Fall-off test. – addresses changing saturation gradients, which has a significant impact on the pressure transients. Schematic saturation profile side view Horner plot example illustrating the effect of banking on an analytical plot
SPE Workshop in Arctic Norway March 11th – 12th 2015 | Harstad, Norway Mitigation #2 Reservoir cooling Issue - cold water reduces formation temperature, hence oil & water viscosities Mitigation – Research show that for pressure transients governed by a moving thermal front, one should use fluid- properties corresponding to the cold injection fluid to analyse the results correctly. – Prior PVT data a plus for job planning – Extensive Fluid Sampling program for Wireline Formation Tests – Bulk sample issue for facilities & pipeline models not solved fully. (Limitation with method) Pressure transient data for injection of 95 °C water into a 250°C reservoir
SPE Workshop in Arctic Norway March 11th – 12th 2015 | Harstad, Norway Generic Pore-pressure & Frac gradient curve Mitigation #3 Formation fracturing Issue – Risk of accidental formation fracturing, possibly fracturing the cap rock. Mitigation – Good control of the Fracture Gradient, plus injectivity modelling before a job. – Requires general good area knowledge. – Possibly that Injection-Fall- off method is best suited for appraisal wells. Example simulation of BHP for Injection Fall-off job
SPE Workshop in Arctic Norway March 11th – 12th 2015 | Harstad, Norway Mitigation #3.1 Formation fracturing - vacuum Other issue – In case a water-injection well is fractured, the wells often go on surface vacuum, where the fluid level can fall below surface, making surface pressure data monitoring impossible. Mitigation – Normally the vacuum would stem from fracture propagation, which limits the issue. However, dealing with this complication requires bottom hole pressure recorders (memory or Surface Read-Out).
SPE Workshop in Arctic Norway March 11th – 12th 2015 | Harstad, Norway Injection Fall-off application It is not recommended to do Injection Fall-off tests for rank exploration wells. However, we would recommend it as a possible Appraisal Well technique, provided the following; – Prior fluid data obtained from earlier exploration wells – Fluid properties available for reduced reservoir temperatures – Sufficient fluid sampling planned on actual well during OH logging – Porosity from earlier cores available – Core saturation experimental results available from earlier wells – Fracture gradient is well known for the target formation
SPE Workshop in Arctic Norway March 11th – 12th 2015 | Harstad, Norway Other To plan a successful Injection Fall-off test the following is needed; – More simulations than normal to model pressure transient responses to ensure correct job design. – A plan for bulk samples for pipeline and facility model experiments Can you live without? Can it be obtained from the Initial Flow period to surface tanks? – Bottom Hole gauges must be used for data gathering. Equipment and services required are the same as for a normal DST, with the exception of Fluid Sampling.
SPE Workshop in Arctic Norway March 11th – 12th 2015 | Harstad, Norway Has it been done before? Source:NPD + Press release – Well bore:7122/7-4S Klappmys Rig:Polar Pioneer Time frame:November 2006 Formation:Kobbe ( m)
SPE Workshop in Arctic Norway March 11th – 12th 2015 | Harstad, Norway Thank you! Arild Fosså | Expro Norway AS