Using drilling data to compare geomechanical parameters with porosity (a case study, South Pars gas field, south of Iran)

摘要

As regards to deficiency or lack of core data and high cost of coring, it was seen necessary to utilize drilling data to study and compare calculated dynamic parameters by log, instead of core data. The elastic modulus of rock includes E (Young's modulus), nu (Poisson's ratio), K (bulk modulus), and G (shear modulus) which are essential geomechanical parameters which are widely used for analysis wellbore stability. In this study, due to the unavailability of the core data, the weight on bit (WOB) was used to compare the rock strength parameters instead of core data. These parameters were calculated by a DSI (dipole shear sonic imager) tool, RHOB, and NPHI log for the Dalan Formation. As regards, the amount of rock porosity is a direct relationship with rock density, and both parameters are effective on wellbore stability and ROP, the relationship between porosity and rock strength parameters was studied. As regards, the amount of rock strength is effective on ROP and WOB, and according to the availability of WOB data, the calculated parameters were compared with WOB. The results indicated that the value of these parameters has an inverse relationship with the amount of porosity. By investigating the relationship between porosity and elastic modulus, it was found that the elastic modulus decreases with increasing porosity. The comparison of porosity and elastic modules denoted that among elastic modulus, bulk modulus has the highest correlation with porosity, and the Poisson ratio has the least correlation with porosity. The UCS (unconfined compressive stress) calculated with the static Young's modulus showed the best correlation with porosity than the calculated UCS. An essential part of the drilling process is adding force to the drill bit in order to successfully break the rock. Weight on bit is the amount of downward force exerted on the drill bit. The amount of WOB is depending on the rock strength, which is the minimum stress required to fail the rock formation. Comparison of calculating the elastic modulus and UCS with weight on bit illustrated that the calculated UCS with E-s has the best correlation with weight on bit. By comparing the calculated elastic modulus with the weight on bit (WOB), it was found that these parameters are in a good matching with the parameter obtained through drilling and so it can be applied to assess the accuracy of the calculated elastic modulus parameters.