Development Optimisation and Application in a Giant Carbonate Oilfield Under Low Remuneration Fee, Y Oilfield in Iraq
Authors: Hu Dandan , Guo Rui , Feng Mingsheng , Wang Liangshan , Wei Liang , Wu Yuanbing , Luo Yupeng , Tian Ping 
Published: March 2015

Abstract
Y is a giant carbonate oilfield with low permeability and mid-high porosity, of which the characteristic is extensive plane distribution and many series of oil-zones in the longitudinal direction. The service contract required a large scale capacity construction with nearly 30 million ton and long stable production period above 13 years, but provided a low remuneration fee with only 1.4$/bbl. Full oilfield integrated optimization is crucial to achieve high effective development and enhance economic benefit. In this paper, the procedure of research on integrated development optimization was elaborated. The paper established new productivity model with oil-water two phase to accurately evaluate oil well productivity. Depletion mode and zones combination were demonstrated and optimized through core experiments and numerical simulation. The sensitivity studies of well types, well patterns and well spacings were carried out through modelling and empirical formula method. Multifactor analysis was completed with surface engineering and external oil-gas transportation capacity as important factors, and development strategy of rapid productivity construction and rolling development is put forward. Depletion plan for each reservoir has been also optimized based on full reservoir simulation modelling. The recommended depletion plan has been implemented in the oilfield development, of which productivity coincidence rate was nearly 100%, first stage productivity capacity with 5 million ton has been set up in 2012, and IRR increased from 9% to above 13%.

Introduction
Y is a giant carbonate oilfield in Iraq, with huge oil area, massive geological reserves, multiple zones in the vertical direction, varied characteristics in the lateral direction and high well productivity. These carbonate reservoirs have low natural energy and reservoir pressure declines rapidly when depletion drive is adopted, resulting in low recovery. Development optimization is needed, proper measures should be taken to supplement energy, and economic and effective technical plan should be proposed to improve the production rate within contract period and get a high and stable production. Zones are combined and optimal development mode is selected according to the policy in host country of resources and requirement in production and services contract. The type of well and well pattern is determined based on the underground and surface is integrated and optimized. The goal is to maximize the potential of each reservoir and achieve overall development of the oilfield and improve the production rapidly. The key point in economic and efficient development is to improve well production significantly and keep the well production stable for a relative long period of time, with a low profit of 1.4$/bbld in the contract. In order to improve production by dozens of million tons and get a stable production in the long term in Y oilfield, this paper optimizes the overall development plan to minimize the early investment and to achieve progressive development of the oilfiled and maximize the economic benefit. The production of 5 million tons in the first stage, which was started ahead of schedule, and the productivity of 10 million tons, which was achieved in the second stage, provides references and instruction on how to develop similar huge carbonate oilfield.