Calcium carbonate scale inhibition in squeeze treatment by the phosphonate–type scale inhibitors, such as diethylenetriamine penta (methylene phosphonic acid) (DETPMP), ethylene diamine tetra(methyelne phosphonic acid) (EDTMP) or by the mixing of DETPMP, EDTMP and chelants (citric acid (CA), maleic acid (MA), ethylendiamintetraacetic acid (EDTA) has been studied in previous works [5,6]. This paper focused on several aspects concerning calcium carbonate scale inhibition mechanism of DETPMP and of the mixing of DETPMP with trace of chelants by scale morphology on scanning electron microscopy (SEM). From the SEM photos, it can be observed that the presence of the inhibitors, especially with the right ones, causes