Hydraulic Fracture Treatment Design Simulation for the Rotliegendes Formation

Abstract

SPE Members Abstract As an increasing number of gas fields are being developed or are planned to be developed in the permian red beds (Rotliegendes) of northwest Europe, hydraulic fracturing has become a major stimulation method to obtain economic production rates from this tight gas formation. Optimization of stimulation design and its implementation in the field become more crucial in the formation such as Rotliegendes, where a water bearing zone is underlain. The objective of this work was to simulate fracture growth under various conditions so that optimal treatments can be designed and implemented successfully to this tight gas reservoir. Formation rock properties of the payzone and adjoining barriers, fracturing fluid properties and their leakoff coefficients selected were experimentally determined in the laboratory using various Rotliegendes core samples. A 3-D model of Meyer and Associates was used to simulate the fracture length, width, height, proppant transport and settlement, fracture closure, and post-frac performance. The same treatment data were simulated using a 3-D model developed by Palmer and Carroll. Results obtained from the two models are compared on a rational basis. Two field applications are presented to demonstrate the proper design and successful stimulation treatments in the Rotliegendes. Introduction Since the discovery of the giant Dutch Groningen gas field in the north of the Netherlands (discovery well, Slochteren 1, 1959), an increasing number of gas fields are being developed or are planned to be developed in the permian basin of the North Sea, the Netherlands, Denmark, and Western Germany. The permian red beds of northwest Europe (or better known as "Rotliegendes" in Germany) are continental elastic sediments deposited under desert and semi-desert conditions. The mineralogical study of several Rotliegende core samples indicate that the sandstone primarily consists of quartz with minor dolomite, illite, and kaolinite (migrating type clays) and dawsonite (a bladed mineral). The general texture of such rock is shown in Figure 1. The proved and probable reserves of Rotliegendes gas in the North Sea, Netherlands, and Western Germany is estimated to be about 85x 1012 cu.ft. The development of these fields is only possible if the gas production rates can be maximized by effective hydraulic fracture treatments. Optimum fracture treatment techniques can substantially improve the supply of natural gas from these tight gas reservoirs. The effectiveness of hydraulic fracturing in a tight gas reservoir is strongly affected by the geometry of the created fracture. The geometry of a fracture deals with the propped fracture height and areal extent. The intrusion of a fracture from the payzone into the formations lying above and below is a serious concern in a fracture design. Moreover, if the hydraulic fracture is not contained within the producing formation and propagates in both the vertical and lateral directions, failure of the treatment can occur because there is a substantial loss of fracture fluid and proppant used to fracture the unproductive formations. The containment of a fracture within the producing zone is even more important where the underlying zone is water bearing. P. 247^