Horizontal wells with multistage fracturing completion, a relatively mature technology, have been applied to the development of tight/shale reservoirs for years. However, it still remains an industry challenge to reasonably predict future production profiles and expected ultimate recoveries (EURs) in very tight wells. Recently, a number of new methods, being either empirical or analytical, have been introduced to the industry. However, doubts have been raised for their suitability in wells having production history less than 2 to 3 years.
This paper presents an improved method based on Valko's Stretch Exponential Production Decline (SEPD) by employing a new specialized plot to find all parameters that are essential to production forecast. This newly developed method (also called the Modified SEPD Method or YM-SEPD Method) is much easier to use, and most importantly it will yield a more reliable production forecast and EUR estimation in wells having very short production history, compared to all other currently available methods.
Hundreds of horizontal wells including both oil and gas wells, from various formations (Cadomin, Montney, Notikewin, Cardium, Barnett Shale etc.) and under different hydraulic fracturing conditions, have been analyzed using this YM-SEPD Method. Results have indicated that both EURs and production forecasts can be easily predicted for wells having two to three years of production history. For wells having less than 2 years of production history, this YM-SEPD method will also be able to yield a reasonable production prediction by coupling it with another empirical method.
A close examination on characteristics of the production decline curve, derived from this YM-SEPD method, has revealed the reasons of why this improved method can better predict production performance and EUR in tight horizontal wells. Furthermore, this YM-SEPD method can also provide a very useful mean of identifying the PSS flow of horizontal wells in very tight reservoirs.
Both real and synthetic oil & gas well examples are presented in the paper to illustrate the advantages of using this improved method.
Production profile forecasting and its final expected ultimate recovery (EUR) prediction are the most important part of work in the economic evaluation of development wells. Recent development in horizontal wells with multi-stage fracturing has widely promoted the development of extremely tight (shale) gas reservoirs which was thought to be not economic. However, this growing development also has brought forth great challenges to the reservoir engineers in the prediction of production profiles and EURs.