Abstract Two-dimension multi-phase fluid flow numerical simulations which include drilling fluid, injected gas, formation fluids and cuttings were carried out for different well geometry taking into account both inlets and outlets throughout boundary system. Simulations were made for fields whose formation and fracture pressure profiles are characteristic of the naturally fractured Mexican fields. During simulations different gas injection systems to get underbalanced conditions such as parasite tubing string, annular gas injection and drill-pipe gas injection were proved in order to establish their feasibility for application in the case of study. Pressure and velocity fields together with phase distribution along the well are analyzed in each case to determine their technical and operative applicability as well as to evaluate advantages or disadvantages of this technique respect to the present circumstances during drilling. From the results it is possible affirm that drill-pipe gas injection is the best option to get underbalanced conditions during drilling as is explain in the extent work. A comparative survey against other model results (R.R. Angel, Machado-Ikoku, Poettmann & Berman and Okpöribi) is realized in the final of this work from which it is possible to observe the improvements of this work in regarding those of obtained by mentioned models. According to observed results underbalanced drilling is a good-available solution to total lost circulation and formation damage problems faced presently during drilling-wells in the naturally fractured low-pressure Mexican fields. The main contributions of this work consist of its capability to design drilling performance and quantify lost circulation by means of numerical simulation of volume-average general mass and momentum conservation equations.
Introduction The most important mexican naturally fractured reservoirs are offshore. These reservoirs are compound for high fractured limestones and dolomites with 5 darcys of permeability. Furthermore, some of these, due to exploitation, are depleted.
Fractures, caverns and vugully in these zones causes total lost circulation of drilling fluid. This frequently causes that operator drilling without fluid circulation (blind drilling), only uses viscous slugs of drilling fluid to reach the target.
Partial and total lost circulation of mud control originate formation damage due to fluids and solids invasion into the formation, reducing well productivity and increasing the probability to make stimulations and the well cost.
This paper proposes to use underbalanced drilling technique as a solution to total lost circulation problem. Furthermore, we analyzed and suggested:Fluid type.
Underbalanced drilling technique.
Flow conditions.
Drilling fluid analysis. From an analysis [1] of the most important offshore field of Mexico, has been established that the total lost circulation zone are located in Paleocene and Cretaceous formations, these varies with depth accordingly to structural position of each well. However, in this work a mean interval was established from 5900 to 9520 ft in order to do the analysis.
Using production's data at the lost circulation depth was estimated a pore pressure gradient of 34 lb/ft in units of equivalent density. Hence, to drill from 5900 to 9520 ft, is necessary to establish as boundary of the system a circulation pressure lower than equivalent circulation density previously established.