Modeling Terminal Decline Rate in Flow Regime Transition using AlternatingConditional Expectation Non-Linear Regression Methods

摘要

Accurate EUR estimation is a critical component of the oil and gas asset evaluation process and has becomeincreasingly important in de-risking investments in shale plays. Hybridized decline curve analysis hasemerged as an industry-wide best practice for this process. This method of interpretation is dependent on theaccuracy of the estimated terminal decline rate or switch point. Accurately predicting the terminal declinerate for wells with insufficient production history, has proven difficult. This issue is further aggravatedin emerging basins and regions of development, as well as complications associated with parent-childrelationships in developed acreages. The present paper tackles these challenges by using a statisticalapproach to predict the switch point and onset of terminal decline rates in unconventional shale plays. Typical production profiles in unconventional shales are marked by high initial declines and long transientflow regimes, followed by a transition to boundary dominated flow as the pressure transient reaches theboundaries of the effected reservoir. The decline rate at this switch point, as well as the duration to getto it can vary significantly and is dependent on a wide range of variables. The present paper tacklesthis multivariable problem by using an ACE (alternating conditional expectation) non-linear regressionmodel to predict the switch point. Variables used to predict this change in flow regime include: GammaRay, Resistivity (Deep), RHOB, NPHI, formation thickness, WOR, GOR, completion design, proppantamount per foot, perforated interval, and production performance amongst others. In order to account forthe impact on production, behavior from infill development and parent-child relationship discrepancies,date- dependent 3D well spacing was calculated and incorporated as a variable in the statistical model. Thisprocess was tested and applied to a large dataset of wells in the middle Bakken formation in the WillistonBasin.