First Application in Mexico and New World Depth Record for MPD Concentric Nitrogen Injection to Drill Horizontal Wells in Low Pressure Reservoirs at Samaria Field

Abstract

Samaria oilfield, located in southern Mexico 20 km west of Villahermosa, Tabasco, with an area of about 160 km2 is one of the world's largest in extension and one of the oldest oilfields in Mexico, historic crude oil exploitation targets the Cretaceous Upper Medium and Lower (4200 mts TVD to 4500 mts TVD). Formation pressure in these naturally fractured carbonates has been decreasing over the last 20 years with current values down to 0.4 gr/cc. Managed Pressure Drilling (MPD) techniques are implemented using Nitrogen injected through Drill Pipe to avoid lost circulation, formation damage and differential sticking. However the significant amount of nitrogen inside the DP generates important limitations for current MWD tools. The need for Horizontal wells to increase the drainage area has become a priority for the Mexican National oil company thus directional control and LWD capabilities must be prioritized. The nitrogen concentric injection technique was then taken into consideration to bring solutions to the MWD pulse signal transmission and downhole temperature handicaps. This paper describes the experience gained in planning and executing the first horizontal well in the Samaria field using Nitrogen Concentric String injection also recorded as the deepest ever concentric injection point (4171 mts MD and 4117 mts TVD). The paper will guide the technical community over the design, planning and execution process: geological review and candidate selection, pre-engineering study, transient and steady state multiphase flow modeling, final drilling program, training, safety, contingencies, directional planning for geo-steering with MWD/LWD, lessons learned and production enhancement results. Introduction Antonio J Bermúdez complex was discovered back in 1973. It produces from carbonates sequences from Mesozoic, Cretaceous and Jurassic ages and has been divided into five fields: Samaria, Cunduacan, Iride, Oxiacaque y Platanal and approximately 64 faulted blocks. Figure 1 shows the geographic location of the complex A. J. Bermúdez. Up to date, 342 wells have been drilled to Mesozoic formations and 90 wells to Tertiary. Currently 105 wells are producing from Mesozoic and 4 from Tertiary for a total of 145,194 BOPD and 310 MMSCF. Recently, in the SAMARIA field several projects have been carried out in order to improve productivity by drilling horizontal wells in low pressure (depleted) formations. Being a mature field, SAMARIA production reservoirs pressure average 0.40 gr/cc in highly fractured carbonates. An additional constraint is the rise of the WOC. In this scenario, drilling horizontal wells is a good opportunity to optimize production reducing the chances for water conning. On the other hand, current conditions of the field represent a technological challenge for horizontal drilling due to the difficulties to keep directional control (down hole tools communications) thru these depleted highly fractured reservoirs.