With the increasing volatility in the price of oil, even low-cost onshore wells can be economically marginal and not achieve target rates of return under certain oil price scenarios such as P10 or even P50 production profile forecasts. If such market conditions persist, it will become increasingly important that all wells produce to their full potential and that war be waged on skin and that drainage area be maximized. Where wells are fractured, maximizing fracture conductivity and half-length will also be essential. The author believes that this macro-economic environment will drive an increase in pressure transient analysis (PTA) complemented by rate transient analysis (RTA) because, just as Lord kelvin stated in 1883, “what we cannot measure, we cannot improve”.
Traditionally PTA requires build-ups, which is costly, both in terms of intervention and deferred production. Fortunately, the population of permanent downhole gauges does not cease to increase and this presentation examines how downhole real-time pressure and rate data enables PTA in drawdown. Such technology not only provides a source of low-cost transient data, but also the ability to obtain inflow characterization (mobility, skin, fracture half-length and conductivity and boundary conditions) within a few weeks of completing a well, thereby confirming the time value of information.
To illustrate the concepts, PTA and RTA results from a MFHW (Multi Fractured Horizontal Well) case study are reviewed. This is based on data taken from URTEC 2790 paper and is particularly interesting as it demonstrates how high-quality production data can resolve a large number of unknowns. Also, the history matching of flowing pressure with an analytical model yielded excellent results despite many discreet changes in flow rate, which further enhanced confidence in the inflow characterization. Therefore, if PTA can be performed in drawdown on a complex MFHW in unconventional tight formations, it is relatively easy to achieve on conventional vertical wells. This workflow was applied to over 38 wells in the Bakken to generate a correlation of PV (Pore Volume) and PI (Productivity Index) as a function of completion and fracture design thereby providing quantifiable feedback on how to drill and complete “winning” wells in a particular geological environment.
As always, economic constraints often stimulate technological creativity, and the author predicts that it will not be long before PTA in drawdown is industrialized and applied to SRP and free flowing wells with the addition of a downhole tools such as a venturis. The author hypothesizes that, even in a low oil price environment, economic production is possible if production is optimized utilizing the right instrumentation and interpretation techniques?
PTA in drawdown works when downhole pressure and rate are measured simultaneously with high frequency, high resolution and high repeatability.
- No deferred production associated with build-ups
- Reduce the cost of intervention associated with well testing … if one discounts the cost of instrumentation and SCADA, it is zero
- No wellbore storage and no need for downhole shut-in tools
- Can identify bi-linear flow and therefore distinguish between fracture conductivity and wellbore skin.