Technical Committee Drilling and Completion Technology

Development of CaO-Swelling Cements for Cementing of Natural Gas Underground Storage Wells in Field Trial (Temperature Range ≤ 60 °C), and Composition of CaO- and MgO-Swelling Cements for a Temperature Range between 60 °C-105 °C

The investigations conducted within the scope of this project are a consistent continuation of the work already performed at ITE, especially DGMK research projects 444-1, 444-2 and 444-3. These investigations should lead to a field trial of selected CaO- swelling cement recipes. Essential parameters examined within the course of this project include the HPHT-consistency behavior, HPHT-expansion behavior and the long-term stability behavior of CaO-swelling cements under similar conditions to those prevailing in the borehole. The swelling cement will be made up in correlation with the appropriate industrial make up method using the ITE-equipment; in accordance to the borehole conditions, the swelling cement slurry will be then treated in the ITE-Circulating Facility with respect to shear, temperature and pressure.
The cement slurry treated in the ITE-Circulating Facility in accordance to the borehole conditions will be then experimentally investigated regarding the HPHT-consistency behavior and HPHT-expansion behavior. With respect to the long-term stability the swelling cement slurry treated in the Circulating Facility will be cured in autoclaves under appropriate pT-conditions. After evacuation from the autoclaves the compressive strength, the shear strength and the system permeability of the samples will be measured.
With respect to the properties of a CaO-reference swelling cement recipe measured under the same experimental conditions, the ITE-make up method has been correlated to the common industrial make up methods LPHM, LPRM and HPRM; the alignment of the ITE-make up method with the planned industrial make up method for an appropriate cement job should make sure that the properties of a swelling cement measured in lab will be of practice relevance.
For filling in and annular cementing of selected boreholes CaO-swelling cement recipes have been composed, optimized after experimental investigation results, and ultimately released to field usage after the results of their investigations regarding the longterm stability were positively assessed.
While the planned annular cementing of the selected boreholes has already been completed, the filling in of the other selected boreholes is still to be undertaken. A comparison between the lab experimental results of the selected CaO-swelling cement recipe with the experimental results completed on-site - the latter measurements have been undertaken on samples, which have been taken out from the industrially made up CaO-swelling cement slurry of the same recipe - has led to the recognition that a humidity extraction from the air by the calcium oxide during the blending process and/or during a longer period of the blend's storage in silos has to be avoided in order to preserve the initial swelling potential of the recipe.
The right composition of a CaO- or MgO-swelling cement recipe to be used within a temperature range between 60 [°C] and 105 [°C] presupposes the availability of appropriately reactive swelling agents and the right retarders. While different reactive calcium oxides are offered on the market, more reactive magnesium oxides are not available. Therefore, this topic can still not be answered in conclusion.