Replacing Wireline Formation Pressure With Formation Pressure While Drilling in Long Horizontal Wells
Authors: Denney Dennis 
Published: February 2015

This article, written by Senior Technology Editor Dennis Denney, contains highlights of paper IPTC 12103, "Replacing Wireline Formation Pressure With Formation Pressure While Drilling in Long Horizontal Wells," by J.K. Larsen, SPE, Maersk Oil Qatar; C.J. Maeso, SPE, and F. Liu, SPE, Schlumberger; and R. Narayanan and R. Noman, SPE, Qatar Petroleum, prepared for the 2008 International Petroleum Technology Conference, Kuala Lumpur, 3-5 December. The paper has not been peer reviewed.
A case history presents how formation-pressure-while-drilling (FPWD) technology effectively has replaced traditional pipe-conveyed wireline technology in long horizontal wells. The Al Shaheen field, offshore Qatar, in the Middle East, is developed with 20,000- to 30,000 ft-long horizontal wells, drilled in radial and line-drive patterns in one sandstone and two carbonate reservoirs. Eleven FPWD jobs were performed within the first year, and FPWD now is the preferred option for formation-pressure acquisition in Al Shaheen.

Introduction
Knowledge of the reservoir pressure is essential for understanding the behavior of the reservoir fluids. Fluid gradients are used to establish fluid contacts in the reservoir, and pressure data obtained during the production phase reveal important information about drive mechanisms and the geology. Traditionally, wireline formation testers have been used to obtain formation pressures. FPWD tools have advantages and disadvantages compared to wireline formation testers, depending on the type of well and the objectives of the logging program. Understanding these advantages and disadvantages and the objectives of the logging program is required, and is best achieved through a joint effort by the operator and the service company. The full-length paper details the transition of, and the considerations associated with, introducing FPWD in the Al Shaheen field.

Al Shaheen Field
The Al Shaheen field is a low-relief structure with an areal extent of approximately 40×60 km and is developed in three main reservoirs: Nahr Umr, Shuaiba, and Kharaib (known as Thamama B elsewhere in the region). The Nahr Umr formation is a thin sandstone reservoir normally less than 15 ft thick, with a target zone less than 3 ft thick. The high-permeability target zone often is unconsolidated. The Shuaiba formation is a highly heterogeneous carbonate reservoir with large permeability contrasts associated with facies changes. The Kharaib formation is a tight carbonate reservoir with uniform reservoir properties across the field. The Kharaib permeability ranges from 1 to 10 md.
The 20,000- to 30,000 ft-long horizontal wells are drilled with geosteering to control the position of the wells in the reservoir. Optimal well spacing ranges from 600 ft in the tight Kharaib formation to 2,000 ft in the high-permeability Nahr Umr sandstone. Fig. 1 shows the well placement in the three reservoirs in the northeastern part of the Al Shaheen field. Water injection is used extensively for pressure maintenance in all three reservoirs.