Josip Sečen, DSc
Editor-in-Chief
"Nafta" journal

 

Message to the Readers

Triggered by EU Administration plans and by plans of other world planners regarding production and consumption increase of renewable energy sources and by the latest BP Statistical Review of World Energy - June 2012 that I have already summarized and published in last double issue of this journal, I am forced to inform our respectable readers on the achieved realization of plans.
In 2011, renewable energy consumption in the world made only 1.6% of the total primary energy consumption. It is mostly used in USA (0.37%), Germany (0.19%), China (0.14%), Spain (0.10%), India (0.070%) and Italy (0.06% of total world primary energy consumption).

Electric power was mostly produced by wind power plants: in Spain (8.2% of total domestic consumption of primary energy) followed by Germany (6.7%), Italy (4.3%), India (4.3%), USA (0.7%) and China (0.6%).
USA is leading in biofuel consumption followed by Brazil where in 2011 the production decreased by 15.3% due to poor sugar harvest.
For now, this is a real picture of renewable energy sources that are depending on climate conditions (according to Policy Research Institute the production of biofuels increased the price of basic wheat products by 30% along with the number of hungry people in the world) and wind activity producing electricity at higher price than electricity produced in classic power plants.

Let us move on to the papers published in this double issue. Along with information from oil and gas exploration, production and refining, we are also publishing three papers.

The first one was written by Ehsan Zamanian and associates titled "Determination of Gas-Diffusion and Interface- Mass-Transfer Coefficients in Fracture-Heavy Oil Saturated Porous Matrix System". For modeling and simulation of oil recovery from naturally fractured reservoirs during the gas injection process, an accurate value of molecular diffusion coefficient (MDC) of gases from a gas filled fracture into the oil matrix is essential. During the injection of miscible fluids with oil, transport of the injectant and oil are controlled by fracture and matrix properties. Diffusion is significant oil recovery mechanism between matrix and fracture. However, experimentally determined data concerning to gas transfer between fracture-matrix systems by diffusion mechanisms are relatively rare. In this study the pressure-decay method is applied to obtain effective molecular diffusion coefficient of CO2 and CH4 in heavy oil saturated porous matrix media at different conditions of temperatures. Gas-diffusion and interface-mass-transfer coefficients are determined by applying a transient-state equilibrium diffusion model.

The second paper titled "A Simple Method to Estimate the Maximum Liquid Production Rate Using Plunger Lift System in Wells" was prepared by Alireza Bahadori with associates. Plunger lift is a cyclic method of artificial lift that uses a plunger to establish an interface between the liquid accumulated in the production tubing and the reservoir or annulus gas pressure that will be used to lift the fluid in wells. In this work, the maximum possible liquid production rate that plunger lift will tolerate for a given depth and tubing size has been placed on a quantitative basis by means of simple equations obtained from correlations of field data. The predictive tool developed in this study can be of immense practical value for petroleum engineers to have a quick check on maximum possible liquid production rate that plunger lift will tolerate under given conditions.

The third paper was prepared by I. Billege and associates titled "Natural Gas Consumption in Croatian Refineries 2013 - 2023". Under current circumstances, oil refineries need to remain competent and sustained while faced with the need of continuous technical-technological modernization. Croatian refineries are also faced with the same general status and trends where their geographical position and connection with other oil and gas pipelines make a realistic potential of current and future sustainability. Modernization of refineries could provide Croatia with reliable supply of high quality motor gasoline, diesel fuels and fluid oil gas. According to official modernization plan for Sisak and Rijeka refineries, the natural gas consumption is directed partly as fuel gas with refinery dry gas in processing and partly as feedstock for hydrogen generation in highly demanding treatment of gasoline and diesel, primarily in sulfur recovery process. Having in mind a specific type and way of their modernization, specific natural gas consumption for the stated period was also analyzed in this paper.
At the end of this year, please accept my best wishes for Christmas and New Year holidays and let that spirit follow you throughout 2013. I hope that all your wishes will come true - mostly health and pleasure in professional and private life.